Proofs of Some Conjectures of Chan on Appell-Lerch Sums

Abstract

On page 3 of his lost notebook, Ramanujan defines the Appell-Lerch sum $$\varphi (q):=\sum _{n=0}^{\infty }\frac{(-q;q{)}_{2n}{q}^{n+1}}{(q;q^2{)}_{n+1}^2},$$ which is connected to some of his sixth order mock theta functions. Let ${\sum }_{n=1}^{\infty }a(n)q^n:=\varphi (q)$. In this paper, we find a representation of the generating function of $a(10n+9)$ in terms of $q$-products. As corollaries, we deduce the congruences $a(50n+19)\equiv a(50n+39)\equiv a(50n+49)\equiv 0(\text{mod}25)$ as well as $a(1250n+250r+219)\equiv 0(\text{mod}125)$, where $r=1$, $3$, and $4$. The first three congruences were conjectured by Chan in 2012, whereas the congruences modulo 125 are new. We also prove two more conjectural congruences of Chan for the coefficients of two Appell-Lerch sums.

14 pages

References in corpus (2)

• Mock Theta Functions
• Transformation Formula of the "2nd" Order Mock Theta Function

Cited by in corpus (1)

• Results on some partition functions arising from certain relations involving the Rogers-Ramanujan continued fractions