Euler's constant

"Euler's constant" redirects here. For the base of the natural logarithm, e ≈ 2.718..., see e (mathematical constant).

The area of the blue region converges to the Euler–Mascheroni constant.

The Euler–Mascheroni constant (also called Euler's constant) is a mathematical constant recurring in analysis and number theory, usually denoted by the lowercase Greek letter gamma (γ).

It is defined as the limiting difference between the harmonic series and the natural logarithm:

${\begin{aligned}\gamma &=\lim _{n\to \infty }\left(-\ln n+\sum _{k=1}^{n}{\frac {1}{k}}\right)\\[5px]&=\int _{1}^{\infty }\left(-{\frac {1}{x}}+{\frac {1}{\lfloor x\rfloor }}\right)\,dx.\end{aligned}}$

Here, $\lfloor x\rfloor$ represents the floor function.

The numerical value of the Euler–Mascheroni constant, to 50 decimal places, is:

0.57721566490153286060651209008240243104215933593992... (sequence A001620 in the OEIS)

Unsolved problem in mathematics:

Is Euler's constant irrational? If so, is it transcendental?

(more unsolved problems in mathematics)

Binary	0.1001001111000100011001111110001101111101...
Decimal	0.5772156649015328606065120900824024310421...
Hexadecimal	0.93C467E37DB0C7A4D1BE3F810152CB56A1CECC3A...
Continued fraction	[0; 1, 1, 2, 1, 2, 1, 4, 3, 13, 5, 1, 1, 8, 1, 2, 4, 1, 1, ...] (It is not known whether this continued fraction is finite, infinite periodic or infinite non-periodic. Shown in linear notation) Source: Sloane

History

The constant first appeared in a 1734 paper by the Swiss mathematician Leonhard Euler, titled De Progressionibus harmonicis observationes (Eneström Index 43). Euler used the notations C and O for the constant. In 1790, Italian mathematician Lorenzo Mascheroni used the notations A and a for the constant. The notation γ appears nowhere in the writings of either Euler or Mascheroni, and was chosen at a later time perhaps because of the constant's connection to the gamma function. For example, the German mathematician Carl Anton Bretschneider used the notation γ in 1835 (Bretschneider 1837, "γ = c = 0,577215 664901 532860 618112 090082 3.." on p. 260) and Augustus De Morgan used it in a textbook published in parts from 1836 to 1842 (De Morgan 1836–1842, "γ" on p. 578)

Appearances

The Euler–Mascheroni constant appears, among other places, in the following ('*' means that this entry contains an explicit equation):

• Expressions involving the exponential integral*
• The Laplace transform* of the natural logarithm
• The first term of the Laurent series expansion for the Riemann zeta function*, where it is the first of the Stieltjes constants*
• Calculations of the digamma function
• A product formula for the gamma function
• The asymptotic expansion of the gamma function for small arguments.
• An inequality for Euler's totient function
• The growth rate of the divisor function
• In dimensional regularization of Feynman diagrams in quantum field theory
• The calculation of the Meissel–Mertens constant
• The third of Mertens' theorems*
• Solution of the second kind to Bessel's equation
• In the regularization/renormalization of the harmonic series as a finite value
• The mean of the Gumbel distribution
• The information entropy of the Weibull and Lévy distributions, and, implicitly, of the chi-squared distribution for one or two degrees of freedom.
• The answer to the coupon collector's problem*
• In some formulations of Zipf's law
• A definition of the cosine integral*
• Lower bounds to a prime gap
• An upper bound on Shannon entropy in quantum information theory (Caves & Fuchs 1996)

Properties

The number γ has not been proved algebraic or transcendental. In fact, it is not even known whether γ is irrational. Using a continued fraction analysis, Papanikolaou showed in 1997 that if γ is rational, its denominator must be greater than 10²⁴⁴⁶⁶³. The ubiquity of γ revealed by the large number of equations below makes the irrationality of γ a major open question in mathematics. Also see (Sondow 2003a).

However, some progress was made. Kurt Mahler showed in 1968 that the number ${\frac {\pi }{2}}{\frac {Y_{0}(2)}{J_{0}(2)}}-\gamma$ is transcendental (here, $J_{\alpha }(x)$ and $Y_{\alpha }(x)$ are Bessel functions). In 2009 Alexander Aptekarev proved that at least one of the Euler–Mascheroni constant γ and the Euler–Gompertz constant δ is irrational. This result was improved in 2012 by Tanguy Rivoal, who proved that at least one of them is transcendental.

In 2010 M. Ram Murti and N. Saradha considered an infinite list of numbers containing ⁠γ/4⁠ and showed that all but at most one of them are transcendental. In 2013 M. Ram Murti and A. Zaytseva again considered an infinite list of numbers containing γ and showed than all but at most one are transcendental.

Relation to gamma function

γ is related to the digamma function Ψ, and hence the derivative of the gamma function Γ, when both functions are evaluated at 1. Thus:

$-\gamma =\Gamma '(1)=\Psi (1).$

This is equal to the limits:

${\begin{aligned}-\gamma &=\lim _{z\to 0}\left(\Gamma (z)-{\frac {1}{z}}\right)\\&=\lim _{z\to 0}\left(\Psi (z)+{\frac {1}{z}}\right).\end{aligned}}$

Further limit results are (Krämer 2005):

${\begin{aligned}\lim _{z\to 0}{\frac {1}{z}}\left({\frac {1}{\Gamma (1+z)}}-{\frac {1}{\Gamma (1-z)}}\right)&=2\gamma \\\lim _{z\to 0}{\frac {1}{z}}\left({\frac {1}{\Psi (1-z)}}-{\frac {1}{\Psi (1+z)}}\right)&={\frac {\pi ^{2}}{3\gamma ^{2}}}.\end{aligned}}$

A limit related to the beta function (expressed in terms of gamma functions) is

${\begin{aligned}\gamma &=\lim _{n\to \infty }\left({\frac {\Gamma \left({\frac {1}{n}}\right)\Gamma (n+1)\,n^{1+{\frac {1}{n}}}}{\Gamma \left(2+n+{\frac {1}{n}}\right)}}-{\frac {n^{2}}{n+1}}\right)\\&=\lim \limits _{m\to \infty }\sum _{k=1}^{m}{m \choose k}{\frac {(-1)^{k}}{k}}\ln {\big (}\Gamma (k+1){\big )}.\end{aligned}}$

Relation to the zeta function

γ can also be expressed as an infinite sum whose terms involve the Riemann zeta function evaluated at positive integers:

${\begin{aligned}\gamma &=\sum _{m=2}^{\infty }(-1)^{m}{\frac {\zeta (m)}{m}}\\&=\ln {\frac {4}{\pi }}+\sum _{m=2}^{\infty }(-1)^{m}{\frac {\zeta (m)}{2^{m-1}m}}.\end{aligned}}$

Other series related to the zeta function include:

${\begin{aligned}\gamma &={\tfrac {3}{2}}-\ln 2-\sum _{m=2}^{\infty }(-1)^{m}\,{\frac {m-1}{m}}{\big (}\zeta (m)-1{\big )}\\&=\lim _{n\to \infty }\left({\frac {2n-1}{2n}}-\ln n+\sum _{k=2}^{n}\left({\frac {1}{k}}-{\frac {\zeta (1-k)}{n^{k}}}\right)\right)\\&=\lim _{n\to \infty }\left({\frac {2^{n}}{e^{2^{n}}}}\sum _{m=0}^{\infty }{\frac {2^{mn}}{(m+1)!}}\sum _{t=0}^{m}{\frac {1}{t+1}}-n\ln 2+O\left({\frac {1}{2^{n}\,e^{2^{n}}}}\right)\right).\end{aligned}}$

The error term in the last equation is a rapidly decreasing function of n. As a result, the formula is well-suited for efficient computation of the constant to high precision.

Other interesting limits equaling the Euler–Mascheroni constant are the antisymmetric limit (Sondow 1998):

${\begin{aligned}\gamma &=\lim _{s\to 1^{+}}\sum _{n=1}^{\infty }\left({\frac {1}{n^{s}}}-{\frac {1}{s^{n}}}\right)\\&=\lim _{s\to 1}\left(\zeta (s)-{\frac {1}{s-1}}\right)\\&=\lim _{s\to 0}{\frac {\zeta (1+s)+\zeta (1-s)}{2}}\end{aligned}}$

and de la Vallée-Poussin's formula

$\gamma =\lim _{n\to \infty }{\frac {1}{n}}\,\sum _{k=1}^{n}\left(\left\lceil {\frac {n}{k}}\right\rceil -{\frac {n}{k}}\right)$

where $\lceil \,\rceil$ are ceiling brackets.

Closely related to this is the rational zeta series expression. By taking separately the first few terms of the series above, one obtains an estimate for the classical series limit:

$\gamma =\sum _{k=1}^{n}{\frac {1}{k}}-\ln n-\sum _{m=2}^{\infty }{\frac {\zeta (m,n+1)}{m}},$

where ζ(s,k) is the Hurwitz zeta function. The sum in this equation involves the harmonic numbers, H_n. Expanding some of the terms in the Hurwitz zeta function gives:

$H_{n}=\ln(n)+\gamma +{\frac {1}{2n}}-{\frac {1}{12n^{2}}}+{\frac {1}{120n^{4}}}-\varepsilon ,$

where 0 < ε < ⁠1/252n⁶⁠.

γ can also be expressed as follows where A is the Glaisher–Kinkelin constant:

$\gamma =12\,\log(A)-\log(2\pi )+{\frac {6}{\pi ^{2}}}\,\zeta '(2)$

γ can also be expressed as follows, which can be proven by expressing the zeta function as a Laurent series:

$\gamma =\lim _{n\to \infty }{\biggl (}-n+\zeta {\Bigl (}{\frac {n+1}{n}}{\Bigr )}{\biggr )}$

Integrals

γ equals the value of a number of definite integrals:

${\begin{aligned}\gamma &=-\int _{0}^{\infty }e^{-x}\ln x\,dx\\&=-\int _{0}^{1}\ln \left(\ln {\frac {1}{x}}\right)dx\\&=\int _{0}^{\infty }\left({\frac {1}{e^{x}-1}}-{\frac {1}{x\cdot e^{x}}}\right)dx\\&=\int _{0}^{1}\left({\frac {1}{\ln x}}+{\frac {1}{1-x}}\right)dx\\&=\int _{0}^{\infty }\left({\frac {1}{1+x^{k}}}-e^{-x}\right){\frac {dx}{x}},\quad k>0\\&=2\int _{0}^{\infty }{\frac {e^{-x^{2}}-e^{-x}}{x}}\,dx,\\&=\int _{0}^{1}H_{x}\,dx,\end{aligned}}$

where H_x is the fractional harmonic number.

Definite integrals in which γ appears include:

${\begin{aligned}\int _{0}^{\infty }e^{-x^{2}}\ln x\,dx&=-{\frac {(\gamma +2\ln 2){\sqrt {\pi }}}{4}}\\\int _{0}^{\infty }e^{-x}\ln ^{2}x\,dx&=\gamma ^{2}+{\frac {\pi ^{2}}{6}}.\end{aligned}}$

One can express γ using a special case of Hadjicostas's formula as a double integral (Sondow 2003a) and (Sondow 2005) with equivalent series:

${\begin{aligned}\gamma &=\int _{0}^{1}\int _{0}^{1}{\frac {x-1}{(1-xy)\ln xy}}\,dx\,dy\\&=\sum _{n=1}^{\infty }\left({\frac {1}{n}}-\ln {\frac {n+1}{n}}\right).\end{aligned}}$

An interesting comparison by (Sondow 2005) is the double integral and alternating series

${\begin{aligned}\ln {\frac {4}{\pi }}&=\int _{0}^{1}\int _{0}^{1}{\frac {x-1}{(1+xy)\ln xy}}\,dx\,dy\\&=\sum _{n=1}^{\infty }\left((-1)^{n-1}\left({\frac {1}{n}}-\ln {\frac {n+1}{n}}\right)\right).\end{aligned}}$

It shows that ln ⁠4/π⁠ may be thought of as an "alternating Euler constant".

The two constants are also related by the pair of series (Sondow 2005a)

${\begin{aligned}\gamma &=\sum _{n=1}^{\infty }{\frac {N_{1}(n)+N_{0}(n)}{2n(2n+1)}}\\\ln {\frac {4}{\pi }}&=\sum _{n=1}^{\infty }{\frac {N_{1}(n)-N_{0}(n)}{2n(2n+1)}},\end{aligned}}$

where N₁(n) and N₀(n) are the number of 1s and 0s, respectively, in the base 2 expansion of n.

We have also Catalan's 1875 integral (see Sondow & Zudilin 2006)

$\gamma =\int _{0}^{1}\left({\frac {1}{1+x}}\sum _{n=1}^{\infty }x^{2^{n}-1}\right)\,dx.$

Series expansions

In general,

$\gamma =\lim _{n\to \infty }\left({\frac {1}{1}}+{\frac {1}{2}}+{\frac {1}{3}}+\ldots +{\frac {1}{n}}-\ln(n+\alpha )\right)\equiv \lim _{n\to \infty }\gamma _{n}(\alpha )$

for any $\alpha >-n$. However, the rate of convergence of this expansion depends significantly on $\alpha$. In particular, $\gamma _{n}(1/2)$ exhibits much more rapid convergence than the conventional expansion $\gamma _{n}(0)$ (DeTemple 1993; Havil 2003, pp. 75–78). This is because

${\frac {1}{2(n+1)}}<\gamma _{n}(0)-\gamma <{\frac {1}{2n}},$

while

${\frac {1}{24(n+1)^{2}}}<\gamma _{n}(1/2)-\gamma <{\frac {1}{24n^{2}}}.$

Even so, there exist other series expansions which converge more rapidly than this; some of these are discussed below.

Euler showed that the following infinite series approaches γ:

$\gamma =\sum _{k=1}^{\infty }\left({\frac {1}{k}}-\ln \left(1+{\frac {1}{k}}\right)\right).$

The series for γ is equivalent to a series Nielsen found in 1897 (Krämer 2005, Blagouchine 2016):

$\gamma =1-\sum _{k=2}^{\infty }(-1)^{k}{\frac {\left\lfloor \log _{2}k\right\rfloor }{k+1}}.$

In 1910, Vacca found the closely related series (Vacca 1910, Glaisher 1910, Hardy 1912, Vacca 1925, Kluyver 1927, Krämer 2005, Blagouchine 2016)

${\begin{aligned}\gamma &=\sum _{k=2}^{\infty }(-1)^{k}{\frac {\left\lfloor \log _{2}k\right\rfloor }{k}}\\[5pt]&={\tfrac {1}{2}}-{\tfrac {1}{3}}+2\left({\tfrac {1}{4}}-{\tfrac {1}{5}}+{\tfrac {1}{6}}-{\tfrac {1}{7}}\right)+3\left({\tfrac {1}{8}}-{\tfrac {1}{9}}+{\tfrac {1}{10}}-{\tfrac {1}{11}}+\cdots -{\tfrac {1}{15}}\right)+\cdots ,\end{aligned}}$

where log₂ is the logarithm to base 2 and ⌊ ⌋ is the floor function.

In 1926 he found a second series:

${\begin{aligned}\gamma +\zeta (2)&=\sum _{k=2}^{\infty }\left({\frac {1}{\left\lfloor {\sqrt {k}}\right\rfloor ^{2}}}-{\frac {1}{k}}\right)\\[5pt]&=\sum _{k=2}^{\infty }{\frac {k-\left\lfloor {\sqrt {k}}\right\rfloor ^{2}}{k\left\lfloor {\sqrt {k}}\right\rfloor ^{2}}}\\[5pt]&={\frac {1}{2}}+{\frac {2}{3}}+{\frac {1}{2^{2}}}\sum _{k=1}^{2\cdot 2}{\frac {k}{k+2^{2}}}+{\frac {1}{3^{2}}}\sum _{k=1}^{3\cdot 2}{\frac {k}{k+3^{2}}}+\cdots \end{aligned}}$

From the Malmsten–Kummer expansion for the logarithm of the gamma function (Blagouchine 2014) we get:

$\gamma =\ln \pi -4\ln \left(\Gamma ({\tfrac {3}{4}})\right)+{\frac {4}{\pi }}\sum _{k=1}^{\infty }(-1)^{k+1}{\frac {\ln(2k+1)}{2k+1}}.$

An important expansion for Euler's constant is due to Fontana and Mascheroni

$\gamma =\sum _{n=1}^{\infty }{\frac {|G_{n}|}{n}}={\frac {1}{2}}+{\frac {1}{24}}+{\frac {1}{72}}+{\frac {19}{2880}}+{\frac {3}{800}}+\cdots ,$

where G_n are Gregory coefficients (Krämer 2005, Blagouchine 2016, Blagouchine 2018) This series is the special case $k=1$ of the expansions

${\begin{aligned}\gamma &=H_{k-1}-\ln k+\sum _{n=1}^{\infty }{\frac {(n-1)!|G_{n}|}{k(k+1)\cdots (k+n-1)}}&&\\&=H_{k-1}-\ln k+{\frac {1}{2k}}+{\frac {1}{12k(k+1)}}+{\frac {1}{12k(k+1)(k+2)}}+{\frac {19}{120k(k+1)(k+2)(k+3)}}+\cdots &&\end{aligned}}$

convergent for $k=1,2,\ldots$

A similar series with the Cauchy numbers of the second kind C_n is (Blagouchine 2016; Alabdulmohsin 2018, pp. 147–148)

$\gamma =1-\sum _{n=1}^{\infty }{\frac {C_{n}}{n\,(n+1)!}}=1-{\frac {1}{4}}-{\frac {5}{72}}-{\frac {1}{32}}-{\frac {251}{14400}}-{\frac {19}{1728}}-\ldots$

Blagouchine (2018) found an interesting generalisation of the Fontana-Mascheroni series

$\gamma =\sum _{n=1}^{\infty }{\frac {(-1)^{n+1}}{2n}}{\Big \{}\psi _{n}(a)+\psi _{n}{\Big (}-{\frac {a}{1+a}}{\Big )}{\Big \}},\quad a>-1$

where ψ_n(a) are the Bernoulli polynomials of the second kind, which are defined by the generating function

${\frac {z(1+z)^{s}}{\ln(1+z)}}=\sum _{n=0}^{\infty }z^{n}\psi _{n}(s),\qquad |z|<1,$

For any rational a this series contains rational terms only. For example, at a = 1, it becomes

$\gamma ={\frac {3}{4}}-{\frac {11}{96}}-{\frac {1}{72}}-{\frac {311}{46080}}-{\frac {5}{1152}}-{\frac {7291}{2322432}}-{\frac {243}{100352}}-\ldots$

see OEIS: A302120 and OEIS: A302121. Other series with the same polynomials include these examples:

$\gamma =-\ln(a+1)-\sum _{n=1}^{\infty }{\frac {(-1)^{n}\psi _{n}(a)}{n}},\qquad \Re (a)>-1$

and

$\gamma =-{\frac {2}{1+2a}}\left\{\ln \Gamma (a+1)-{\frac {1}{2}}\ln(2\pi )+{\frac {1}{2}}+\sum _{n=1}^{\infty }{\frac {(-1)^{n}\psi _{n+1}(a)}{n}}\right\},\qquad \Re (a)>-1$

where Γ(a) is the gamma function (Blagouchine 2018).

A series related to the Akiyama-Tanigawa algorithm is

$\gamma =\ln(2\pi )-2-2\sum _{n=1}^{\infty }{\frac {(-1)^{n}G_{n}(2)}{n}}=\ln(2\pi )-2+{\frac {2}{3}}+{\frac {1}{24}}+{\frac {7}{540}}+{\frac {17}{2880}}+{\frac {41}{12600}}+\ldots$

where G_n(2) are the Gregory coefficients of the second order (Blagouchine 2018).

Series of prime numbers:

$\gamma =\lim _{n\to \infty }\left(\ln n-\sum _{p\leq n}{\frac {\ln p}{p-1}}\right).$

Asymptotic expansions

γ equals the following asymptotic formulas (where H_n is the nth harmonic number):

$\gamma \sim H_{n}-\ln n-{\frac {1}{2n}}+{\frac {1}{12n^{2}}}-{\frac {1}{120n^{4}}}+\cdots$ (Euler)

$\gamma \sim H_{n}-\ln \left({n+{\frac {1}{2}}+{\frac {1}{24n}}-{\frac {1}{48n^{3}}}+\cdots }\right)$ (Negoi)

$\gamma \sim H_{n}-{\frac {\ln n+\ln(n+1)}{2}}-{\frac {1}{6n(n+1)}}+{\frac {1}{30n^{2}(n+1)^{2}}}-\cdots$ (Cesàro)

The third formula is also called the Ramanujan expansion.

Alabdulmohsin 2018, pp. 147–148 derived closed-form expressions for the sums of errors of these approximations. He showed that (Theorem A.1):

$\sum _{n=1}^{\infty }\log n+\gamma -H_{n}+{\frac {1}{2n}}={\frac {\log(2\pi )-1-\gamma }{2}}$

$\sum _{n=1}^{\infty }\log {\sqrt {n(n+1)}}+\gamma -H_{n}={\frac {\log(2\pi )-1}{2}}-\gamma$

$\sum _{n=1}^{\infty }(-1)^{n}{\Big (}\log n+\gamma -H_{n}{\Big )}={\frac {\log \pi -\gamma }{2}}$

Exponential

The constant e^γ is important in number theory. Some authors denote this quantity simply as γ′. e^γ equals the following limit, where p_n is the nth prime number:

$e^{\gamma }=\lim _{n\to \infty }{\frac {1}{\ln p_{n}}}\prod _{i=1}^{n}{\frac {p_{i}}{p_{i}-1}}.$

This restates the third of Mertens' theorems (Weisstein n.d.). The numerical value of e^γ is:

1.78107241799019798523650410310717954916964521430343... OEIS: A073004.

Other infinite products relating to e^γ include:

${\begin{aligned}{\frac {e^{1+{\frac {\gamma }{2}}}}{\sqrt {2\pi }}}&=\prod _{n=1}^{\infty }e^{-1+{\frac {1}{2n}}}\left(1+{\frac {1}{n}}\right)^{n}\\{\frac {e^{3+2\gamma }}{2\pi }}&=\prod _{n=1}^{\infty }e^{-2+{\frac {2}{n}}}\left(1+{\frac {2}{n}}\right)^{n}.\end{aligned}}$

These products result from the Barnes G-function.

In addition,

$e^{\gamma }={\sqrt {\frac {2}{1}}}\cdot {\sqrt[{3}]{\frac {2^{2}}{1\cdot 3}}}\cdot {\sqrt[{4}]{\frac {2^{3}\cdot 4}{1\cdot 3^{3}}}}\cdot {\sqrt[{5}]{\frac {2^{4}\cdot 4^{4}}{1\cdot 3^{6}\cdot 5}}}\cdots$

where the nth factor is the (n + 1)th root of

$\prod _{k=0}^{n}(k+1)^{(-1)^{k+1}{n \choose k}}.$

This infinite product, first discovered by Ser in 1926, was rediscovered by Sondow (Sondow 2003) using hypergeometric functions.

It also holds that

${\frac {e^{\frac {\pi }{2}}+e^{-{\frac {\pi }{2}}}}{\pi e^{\gamma }}}=\prod _{n=1}^{\infty }\left(e^{-{\frac {1}{n}}}\left(1+{\frac {1}{n}}+{\frac {1}{2n^{2}}}\right)\right).$

Continued fraction

The continued fraction expansion of γ is of the form [0; 1, 1, 2, 1, 2, 1, 4, 3, 13, 5, 1, 1, 8, 1, 2, 4, 1, 1, 40, ...] OEIS: A002852, which has no apparent pattern. The continued fraction is known to have at least 475,006 terms, and it has infinitely many terms if and only if γ is irrational.

Generalizations

abm(x) = γ_−x

Euler's generalized constants are given by

$\gamma _{\alpha }=\lim _{n\to \infty }\left(\sum _{k=1}^{n}{\frac {1}{k^{\alpha }}}-\int _{1}^{n}{\frac {1}{x^{\alpha }}}\,dx\right),$

for 0 < α < 1, with γ as the special case α = 1 (Havil 2003, pp. 117–118). This can be further generalized to

$c_{f}=\lim _{n\to \infty }\left(\sum _{k=1}^{n}f(k)-\int _{1}^{n}f(x)\,dx\right)$

for some arbitrary decreasing function f. For example,

$f_{n}(x)={\frac {(\ln x)^{n}}{x}}$

gives rise to the Stieltjes constants, and

$f_{a}(x)=x^{-a}$

gives

$\gamma _{f_{a}}={\frac {(a-1)\zeta (a)-1}{a-1}}$

where again the limit

$\gamma =\lim _{a\to 1}\left(\zeta (a)-{\frac {1}{a-1}}\right)$

appears.

A two-dimensional limit generalization is the Masser–Gramain constant.

Euler–Lehmer constants are given by summation of inverses of numbers in a common modulo class (Ram Murty & Saradha 2010):

$\gamma (a,q)=\lim _{x\to \infty }\left(\sum _{0<n\leq x \atop n\equiv a{\pmod {q}}}{\frac {1}{n}}-{\frac {\ln x}{q}}\right).$

The basic properties are

${\begin{aligned}\gamma (0,q)&={\frac {\gamma -\ln q}{q}},\\\sum _{a=0}^{q-1}\gamma (a,q)&=\gamma ,\\q\gamma (a,q)&=\gamma -\sum _{j=1}^{q-1}e^{-{\frac {2\pi aij}{q}}}\ln \left(1-e^{\frac {2\pi ij}{q}}\right),\end{aligned}}$

and if gcd(a,q) = d then

$q\gamma (a,q)={\frac {q}{d}}\gamma \left({\frac {a}{d}},{\frac {q}{d}}\right)-\ln d.$

Published digits

Euler initially calculated the constant's value to 6 decimal places. In 1781, he calculated it to 16 decimal places. Mascheroni attempted to calculate the constant to 32 decimal places, but made errors in the 20th–22nd and 31st-32nd decimal places; starting from the 20th digit, he calculated ...1811209008239 when the correct value is ...0651209008240.

Published Decimal Expansions of γ

Date	Decimal digits	Author	Sources
1734	5	Leonhard Euler
1735	15	Leonhard Euler
1781	16	Leonhard Euler
1790	32	Lorenzo Mascheroni, with 20-22 and 31-32 wrong
1809	22	Johann G. von Soldner
1811	22	Carl Friedrich Gauss
1812	40	Friedrich Bernhard Gottfried Nicolai
1857	34	Christian Fredrik Lindman
1861	41	Ludwig Oettinger
1867	49	William Shanks
1871	99	James W.L. Glaisher
1871	101	William Shanks
1877	262	J. C. Adams
1952	328	John William Wrench Jr.
1961	1050	Helmut Fischer and Karl Zeller
1962	1271	Donald Knuth
1962	3566	Dura W. Sweeney
1973	4879	William A. Beyer and Michael S. Waterman
1977	20700	Richard P. Brent
1980	30100	Richard P. Brent & Edwin M. McMillan
1993	172000	Jonathan Borwein
1999	108000000	Patrick Demichel and Xavier Gourdon
March 13, 2009	29844489545	Alexander J. Yee & Raymond Chan
December 22, 2013	119377958182	Alexander J. Yee
March 15, 2016	160000000000	Peter Trueb
May 18, 2016	250000000000	Ron Watkins
August 23, 2017	477511832674	Ron Watkins
May 26, 2020	600000000100	Seungmin Kim & Ian Cutress

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• Ram Murty, M.; Saradha, N. (2010). "Euler–Lehmer constants and a conjecture of Erdos". JNT. 130 (12): 2671–2681. doi:10.1016/j.jnt.2010.07.004.
• Sloane, N. J. A. (ed.). "Sequence A002852 (Continued fraction for Euler's constant)". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation.
• Sondow, Jonathan (1998). "An antisymmetric formula for Euler's constant". Mathematics Magazine. Vol. 71. pp. 219–220. Archived from the original on 2011-06-04. Retrieved 2006-05-29.
• Sondow, Jonathan (2002). "A hypergeometric approach, via linear forms involving logarithms, to irrationality criteria for Euler's constant". Mathematica Slovaca. 59: 307–314. arXiv:math.NT/0211075. Bibcode:2002math.....11075S. with an Appendix by Sergey Zlobin
• Sondow, Jonathan (2003). "An infinite product for e^γ via hypergeometric formulas for Euler's constant, γ". arXiv:math.CA/0306008.
• Sondow, Jonathan (2003a), "Criteria for irrationality of Euler's constant", Proceedings of the American Mathematical Society, 131 (11): 3335–3344, arXiv:math.NT/0209070, doi:10.1090/S0002-9939-03-07081-3, S2CID 91176597
• Sondow, Jonathan (2005), "Double integrals for Euler's constant and $\ln {\frac {4}{\pi }}$ and an analog of Hadjicostas's formula", American Mathematical Monthly, 112 (1): 61–65, arXiv:math.CA/0211148, doi:10.2307/30037385, JSTOR 30037385
• Sondow, Jonathan (2005a), New Vacca-type rational series for Euler's constant and its 'alternating' analog $\ln {\frac {4}{\pi }}$, arXiv:math.NT/0508042
• Sondow, Jonathan; Zudilin, Wadim (2006). "Euler's constant, q-logarithms, and formulas of Ramanujan and Gosper". The Ramanujan Journal. 12 (2): 225–244. arXiv:math.NT/0304021. doi:10.1007/s11139-006-0075-1. S2CID 1368088.
• Weisstein, Eric W. (n.d.). "Mertens Constant". mathworld.wolfram.com.{{cite web}}: CS1 maint: year (link)

Further reading

• Borwein, Jonathan M.; David M. Bradley; Richard E. Crandall (2000). "Computational Strategies for the Riemann Zeta Function" (PDF). Journal of Computational and Applied Mathematics. 121 (1–2): 11. Bibcode:2000JCoAM.121..247B. doi:10.1016/s0377-0427(00)00336-8. Derives γ as sums over Riemann zeta functions.
• Gerst, I. (1969). "Some series for Euler's constant". Amer. Math. Monthly. 76 (3): 237–275. doi:10.2307/2316370. JSTOR 2316370.
• Glaisher, James Whitbread Lee (1872). "On the history of Euler's constant". Messenger of Mathematics. 1: 25–30. JFM 03.0130.01.
• Gourdon, Xavier; Sebah, P. (2002). "Collection of formulae for Euler's constant, γ".
• Gourdon, Xavier; Sebah, P. (2004). "The Euler constant: γ".
• Karatsuba, E. A. (1991). "Fast evaluation of transcendental functions". Probl. Inf. Transm. 27 (44): 339–360.
• Karatsuba, E.A. (2000). "On the computation of the Euler constant γ". Journal of Numerical Algorithms. 24 (1–2): 83–97. doi:10.1023/A:1019137125281. S2CID 21545868.
• Knuth, Donald (1997). The Art of Computer Programming, Vol. 1 (3rd ed.). Addison-Wesley. ISBN 0-201-89683-4.
• Lerch, M. (1897). "Expressions nouvelles de la constante d'Euler". Sitzungsberichte der Königlich Böhmischen Gesellschaft der Wissenschaften. 42: 5.
• Mascheroni, Lorenzo (1790), Adnotationes ad calculum integralem Euleri, in quibus nonnulla problemata ab Eulero proposita resolvuntur, Galeati, Ticini
• Lehmer, D. H. (1975). "Euler constants for arithmetical progressions" (PDF). Acta Arith. 27 (1): 125–142. doi:10.4064/aa-27-1-125-142.
• Vacca, G. (1926). "Nuova serie per la costante di Eulero, C=0,577...". Rendiconti, Accademia Nazionale dei Lincei, Roma, Classe di Scienze Fisiche". Matematiche e Naturali. 6 (3): 19–20.

External links

• "Euler constant", Encyclopedia of Mathematics, EMS Press, 2001 [1994]
• Weisstein, Eric W. "Euler–Mascheroni constant". MathWorld.
• Jonathan Sondow.
• Fast Algorithms and the FEE Method, E.A. Karatsuba (2005)
• Further formulae which make use of the constant: Gourdon and Sebah (2004).