Integrals, Partitions, and Cellular Automata

Abstract

We prove that $${\int }_0^1\frac{-\log f(x)}{x}dx=\frac{{\pi }^2}{3ab}$$ where $f(x)$ is the decreasing function that satisfies $f^a-f^b=x^a-x^b$, for $0<a<b$. When $a$ is an integer and $b=a+1$ we deduce several combinatorial results. These include an asymptotic formula for the number of integer partitions not having $a$ consecutive parts, and a formula for the metastability thresholds of a class of threshold growth cellular automaton models related to bootstrap percolation.

Revised version. 28 pages, 2 figures