Infinite families of congruences for c(n) modulo 4 and 8
Establish, for all integers k, n ≥ 0, the following congruences for the coefficients c(m) defined by C(q) = Σ_{m≥0} c(m) q^m with C(q) = q A(q) S(q), A(q) = (-q^2; q^2)_∞ / (q; q^2)_∞^2, and S(q) = Σ_{r≥0} (q; q^2)_r^2 q^{2r} / (-q^2; q^2)_r: c(2^{2k+3} n + (11·4^k + 1)/3) ≡ 0 (mod 4); c(2^{2k+3} n + (17·4^k + 1)/3) ≡ 0 (mod 8); c(2^{2k+4} n + (38·4^k + 1)/3) ≡ 0 (mod 4).
References
Conjecture For k,n∈ℕ0, we have c(2{2k+3}n + (11·4k + 1)/3)≡0mod{4}, c(2{2k+3}n + (17·4k + 1)/3)≡0mod{8}, c(2{2k+4}n + (38·4k + 1)/3)≡0mod{4}.
— On congruence conjectures of Andrews and Bachraoui
(2604.02239 - Banerjee et al., 2 Apr 2026) in Section 6 (Open questions)