# Particular values of the Riemann zeta function

(Redirected from Zeta constants)

This article gives some specific values of the Riemann zeta function, including values at integer arguments, and some series involving them.

## The Riemann zeta function at 0 and 1

At zero, one has

$\zeta (0)={B_{1}^{-}}=-{B_{1}^{+}}=-{\tfrac {1}{2}}\!$ At 1 there is a pole, so ζ(1) is not finite but the left and right limits are:

$\lim _{\varepsilon \to 0^{\pm }}\zeta (1+\varepsilon )=\pm \infty$ Since it is a pole of first order, its principal value exists and is equal to the Euler–Mascheroni constant γ = 0.57721 56649+.

## Positive integers

### Even positive integers

For the even positive integers, one has the relationship to the Bernoulli numbers:

$\zeta (2n)=(-1)^{n+1}{\frac {B_{2n}(2\pi )^{2n}}{2(2n)!}}\!$ for $n\in \mathbb {N}$ . The first few values are given by:

$\zeta (2)=1+{\frac {1}{2^{2}}}+{\frac {1}{3^{2}}}+\cdots ={\frac {\pi ^{2}}{6}}=1.6449\dots \!$ ()
(the demonstration of this equality is known as the Basel problem)
$\zeta (4)=1+{\frac {1}{2^{4}}}+{\frac {1}{3^{4}}}+\cdots ={\frac {\pi ^{4}}{90}}=1.0823\dots \!$ ()
(the Stefan–Boltzmann law and Wien approximation in physics)
$\zeta (6)=1+{\frac {1}{2^{6}}}+{\frac {1}{3^{6}}}+\cdots ={\frac {\pi ^{6}}{945}}=1.0173\dots \!$ ()
$\zeta (8)=1+{\frac {1}{2^{8}}}+{\frac {1}{3^{8}}}+\cdots ={\frac {\pi ^{8}}{9450}}=1.00407\dots \!$ ()
$\zeta (10)=1+{\frac {1}{2^{10}}}+{\frac {1}{3^{10}}}+\cdots ={\frac {\pi ^{10}}{93555}}=1.000994\dots \!$ ()
$\zeta (12)=1+{\frac {1}{2^{12}}}+{\frac {1}{3^{12}}}+\cdots ={\frac {691\pi ^{12}}{638512875}}=1.000246\dots \!$ ()
$\zeta (14)=1+{\frac {1}{2^{14}}}+{\frac {1}{3^{14}}}+\cdots ={\frac {2\pi ^{14}}{18243225}}=1.0000612\dots \!$ ().

Taking the limit $n\rightarrow \infty$ , one obtains $\zeta (\infty )=1$ .

The relationship between zeta at the positive even integers and the Bernoulli numbers may be written as

$A_{n}\zeta (2n)=B_{n}\pi ^{2n}\,\!$ where $A_{n}$ and $B_{n}$ are integers for all even $n$ . These are given by the integer sequences and , respectively, in OEIS. Some of these values are reproduced below:

coefficients
n A B
1 6 1
2 90 1
3 945 1
4 9450 1
5 93555 1
6 638512875 691
7 18243225 2
8 325641566250 3617
9 38979295480125 43867
10 1531329465290625 174611
11 13447856940643125 155366
12 201919571963756521875 236364091
13 11094481976030578125 1315862
14 564653660170076273671875 6785560294
15 5660878804669082674070015625 6892673020804
16 62490220571022341207266406250 7709321041217
17 12130454581433748587292890625 151628697551

If we let $\eta _{n}=B_{n}/A_{n}$ be the coefficient of $\pi ^{2n}$ as above,

$\zeta (2n)=\sum _{\ell =1}^{\infty }{\frac {1}{\ell ^{2n}}}=\eta _{n}\pi ^{2n}$ then we find recursively,

{\begin{aligned}\eta _{1}&=1/6\\\eta _{n}&=\sum _{\ell =1}^{n-1}(-1)^{\ell -1}{\frac {\eta _{n-\ell }}{(2\ell +1)!}}+(-1)^{n+1}{\frac {n}{(2n+1)!}}\end{aligned}} This recurrence relation may be derived from that for the Bernoulli numbers.

Also, there is another recurrence:

$\zeta (2n)={\frac {1}{n+{\frac {1}{2}}}}\sum _{k=1}^{n-1}\zeta (2k)\zeta (2n-2k),n>1$ which can be proved, using that ${\frac {d}{dx}}\cot(x)=-1-\cot ^{2}(x)$ The values of the zeta function at non-negative even integers have the generating function:

$\sum _{n=0}^{\infty }\zeta (2n)x^{2n}=-{\frac {\pi x}{2}}\cot(\pi x)=-{\frac {1}{2}}+{\frac {\pi ^{2}}{6}}x^{2}+{\frac {\pi ^{4}}{90}}x^{4}+{\frac {\pi ^{6}}{945}}x^{6}+\cdots$ Since

$\lim _{n\rightarrow \infty }\zeta (2n)=1$ The formula also shows that for $n\in \mathbb {N} ,n\rightarrow \infty$ ,

$\left|B_{2n}\right|\sim {\frac {2(2n)!}{(2\pi )^{2n}}}$ ### Odd positive integers

For the first few odd natural numbers one has

$\zeta (1)=1+{\frac {1}{2}}+{\frac {1}{3}}+\cdots =\infty \!$ (the harmonic series);
$\zeta (3)=1+{\frac {1}{2^{3}}}+{\frac {1}{3^{3}}}+\cdots =1.20205\dots \!$ ()
(Called Apéry's constant and has a role in the electron's gyromagnetic ratio)
$\zeta (5)=1+{\frac {1}{2^{5}}}+{\frac {1}{3^{5}}}+\cdots =1.03692\dots \!$ ()
(Appears in Planck's law)
$\zeta (7)=1+{\frac {1}{2^{7}}}+{\frac {1}{3^{7}}}+\cdots =1.00834\dots \!$ ()
$\zeta (9)=1+{\frac {1}{2^{9}}}+{\frac {1}{3^{9}}}+\cdots =1.002008\dots \!$ ()

It is known that ζ(3) is irrational (Apéry's theorem) and that infinitely many of the numbers ζ(2n + 1) (nN) are irrational. There are also results on the irrationality of values of the Riemann zeta function at the elements of certain subsets of the positive odd integers; for example, at least one of ζ(5), ζ(7), ζ(9), or ζ(11) is irrational.

The positive odd integers of the zeta function appear in physics, specifically correlation functions of antiferromagnetic XXX spin chain.

Most of the identities following below are provided by Simon Plouffe. They are notable in that they converge quite rapidly, giving almost three digits of precision per iteration, and are thus useful for high-precision calculations.

#### ζ(5)

Plouffe gives the following identities

{\begin{aligned}\zeta (5)&={\frac {1}{294}}\pi ^{5}-{\frac {72}{35}}\sum _{n=1}^{\infty }{\frac {1}{n^{5}(e^{2\pi n}-1)}}-{\frac {2}{35}}\sum _{n=1}^{\infty }{\frac {1}{n^{5}(e^{2\pi n}+1)}}\\\zeta (5)&=12\sum _{n=1}^{\infty }{\frac {1}{n^{5}\sinh(\pi n)}}-{\frac {39}{20}}\sum _{n=1}^{\infty }{\frac {1}{n^{5}(e^{2\pi n}-1)}}-{\frac {1}{20}}\sum _{n=1}^{\infty }{\frac {1}{n^{5}(e^{2\pi n}+1)}}\end{aligned}} #### ζ(7)

$\zeta (7)={\frac {19}{56700}}\pi ^{7}-2\sum _{n=1}^{\infty }{\frac {1}{n^{7}(e^{2\pi n}-1)}}\!$ Note that the sum is in the form of a Lambert series.

#### ζ(2n + 1)

By defining the quantities

$S_{\pm }(s)=\sum _{n=1}^{\infty }{\frac {1}{n^{s}(e^{2\pi n}\pm 1)}}$ a series of relationships can be given in the form

$0=A_{n}\zeta (n)-B_{n}\pi ^{n}+C_{n}S_{-}(n)+D_{n}S_{+}(n)\,$ where An, Bn, Cn and Dn are positive integers. Plouffe gives a table of values:

coefficients
n A B C D
3 180 7 360 0
5 1470 5 3024 84
7 56700 19 113400 0
9 18523890 625 37122624 74844
11 425675250 1453 851350500 0
13 257432175 89 514926720 62370
15 390769879500 13687 781539759000 0
17 1904417007743250 6758333 3808863131673600 29116187100
19 21438612514068750 7708537 42877225028137500 0
21 1881063815762259253125 68529640373 3762129424572110592000 1793047592085750

These integer constants may be expressed as sums over Bernoulli numbers, as given in (Vepstas, 2006) below.

A fast algorithm for the calculation of Riemann's zeta function for any integer argument is given by E. A. Karatsuba.

## Negative integers

In general, for negative integers (and also zero), one has

$\zeta (-n)=(-1)^{n}{\frac {B_{n+1}}{n+1}}$ The so-called "trivial zeros" occur at the negative even integers:

$\zeta (-2n)=0\,$ The first few values for negative odd integers are

{\begin{aligned}\zeta (-1)&=-{\frac {1}{12}}\\\zeta (-3)&={\frac {1}{120}}\\\zeta (-5)&=-{\frac {1}{252}}\\\zeta (-7)&={\frac {1}{240}}\\\zeta (-9)&=-{\frac {1}{132}}\\\zeta (-11)&={\frac {691}{32760}}\\\zeta (-13)&=-{\frac {1}{12}}\end{aligned}} However, just like the Bernoulli numbers, these do not stay small for increasingly negative odd values. For details on the first value, see 1 + 2 + 3 + 4 + · · ·.

So ζ(m) can be used as the definition of all (including those for index 0 and 1) Bernoulli numbers.

## Derivatives

The derivative of the zeta function at the negative even integers is given by

$\zeta ^{\prime }(-2n)=(-1)^{n}{\frac {(2n)!}{2(2\pi )^{2n}}}\zeta (2n+1)$ The first few values of which are

{\begin{aligned}\zeta ^{\prime }(-2)&=-{\frac {\zeta (3)}{4\pi ^{2}}}\\[6pt]\zeta ^{\prime }(-4)&={\frac {3}{4\pi ^{4}}}\zeta (5)\\[6pt]\zeta ^{\prime }(-6)&=-{\frac {45}{8\pi ^{6}}}\zeta (7)\\[6pt]\zeta ^{\prime }(-8)&={\frac {315}{4\pi ^{8}}}\zeta (9)\end{aligned}} One also has

$\zeta ^{\prime }(0)=-{\frac {1}{2}}\ln(2\pi )\approx -0.918938533\ldots$ (),
$\zeta ^{\prime }(-1)={\frac {1}{12}}-\ln A\approx -0.1654211437\ldots$ ()

and

$\zeta ^{\prime }(2)={\frac {1}{6}}\pi ^{2}(\gamma +\ln 2-12\ln A+\ln \pi )\approx -0.93754825\ldots$ ()

where A is the Glaisher–Kinkelin constant.

## Series involving ζ(n)

The following sums can be derived from the generating function:

$\sum _{k=2}^{\infty }\zeta (k)x^{k-1}=-\psi _{0}(1-x)-\gamma$ where ψ0 is the digamma function.

$\sum _{k=2}^{\infty }(\zeta (k)-1)=1$ $\sum _{k=1}^{\infty }(\zeta (2k)-1)={\frac {3}{4}}$ $\sum _{k=1}^{\infty }(\zeta (2k+1)-1)={\frac {1}{4}}$ $\sum _{k=2}^{\infty }(-1)^{k}(\zeta (k)-1)={\frac {1}{2}}$ Series related to the Euler–Mascheroni constant (denoted by γ) are

$\sum _{k=2}^{\infty }(-1)^{k}{\frac {\zeta (k)}{k}}=\gamma$ $\sum _{k=2}^{\infty }{\frac {\zeta (k)-1}{k}}=1-\gamma$ $\sum _{k=2}^{\infty }(-1)^{k}{\frac {\zeta (k)-1}{k}}=\ln 2+\gamma -1$ and using the principal value

$\zeta (k)=\lim _{\varepsilon \to 0}{\frac {\zeta (k+\varepsilon )+\zeta (k-\varepsilon )}{2}}$ which of course affects only the value at 1. These formulae can be stated as

$\sum _{k=1}^{\infty }(-1)^{k}{\frac {\zeta (k)}{k}}=0$ $\sum _{k=1}^{\infty }{\frac {\zeta (k)-1}{k}}=0$ $\sum _{k=1}^{\infty }(-1)^{k}{\frac {\zeta (k)-1}{k}}=\ln 2$ and show that they depend on the principal value of ζ(1) = γ.

## Nontrivial zeros

Zeros of the Riemann zeta except negative even integers are called "nontrivial zeros". See Andrew Odlyzko's website for their tables and bibliographies.