A note on congruences for the difference between even cranks and odd cranks (2506.16267v2)

Abstract: Recently, Amdeberhan and Merca proved some arithmetic properties of the crank parity function $C(n)$ defined as the difference between the number of partitions of $n$ with even cranks and those with odd cranks and the sequence $a(n)$ whose generating function is the reciprocal of that of $C(n)$. The function $C(n)$ was first studied by Choi, Kang, and Lovejoy. In this note, we give new elementary proofs of some of their main results and extend them. In particular, we establish Ramanujan-type congruences modulo $5$ and $25$ for certain finite sums involving $C(n)$ and $a(n)$. Our proofs employ the results of Cooper, Hirschhorn, and Lewis, and certain identities involving the Rogers-Ramanujan continued fraction $R(q)$ due to Chern and Tang.