Liouville function

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The Liouville function, denoted by λ(n) and named after Joseph Liouville, is an important function in number theory.

If n is a positive integer, then λ(n) is defined as:

where Ω(n) is the number of prime factors of n, counted with multiplicity (sequence A008836 in the OEIS).

λ is completely multiplicative since Ω(n) is completely additive, i.e.: Ω(ab) = Ω(a) + Ω(b). The number 1 has no prime factors, so Ω(1) = 0 and therefore λ(1) = 1. The Liouville function satisfies the identity:

The Liouville function's Dirichlet inverse is the absolute value of the Möbius function.


The Dirichlet series for the Liouville function is related to the Riemann zeta function by

The Lambert series for the Liouville function is

where is the Jacobi theta function.


Summatory Liouville function L(n) up to n = 104. The readily visible oscillations are due to the first non-trivial zero of the Riemann zeta function.
Summatory Liouville function L(n) up to n = 107. Note the apparent scale invariance of the oscillations.
Logarithmic graph of the negative of the summatory Liouville function L(n) up to n = 2 × 109. The green spike shows the function itself (not its negative) in the narrow region where the Pólya conjecture fails; the blue curve shows the oscillatory contribution of the first Riemann zero.
Harmonic Summatory Liouville function T(n) up to n = 103

The Pólya conjecture is a conjecture made by George Pólya in 1919. Defining

(sequence A002819 in the OEIS),

the conjecture states that for n > 1. This turned out to be false. The smallest counter-example is n = 906150257, found by Minoru Tanaka in 1980. It has since been shown that L(n) > 0.0618672n for infinitely many positive integers n,[1] while it can also be shown via the same methods that L(n) < -1.3892783n for infinitely many positive integers n.[2]

Define the related sum

It was open for some time whether T(n) ≥ 0 for sufficiently big nn0 (this conjecture is occasionally–though incorrectly–attributed to Pál Turán). This was then disproved by Haselgrove (1958), who showed that T(n) takes negative values infinitely often. A confirmation of this positivity conjecture would have led to a proof of the Riemann hypothesis, as was shown by Pál Turán.


  1. ^ P. Borwein, R. Ferguson, and M. J. Mossinghoff, Sign Changes in Sums of the Liouville Function, Mathematics of Computation 77 (2008), no. 263, 1681–1694.
  2. ^ Peter Humphries, The distribution of weighted sums of the Liouville function and Pólya’s conjecture, Journal of Number Theory 133 (2013), 545–582.