Conjectured period-five sign patterns for coefficients of Rogers-Ramanujan products

Let R(q)R(q) denote the Rogers–Ramanujan continued fraction, and define integer sequences A(n)A(n), B(n)B(n), and D(n)D(n) by

1R5(q)=n0A(n)qn,R5(q)=n0B(n)qn,R(q5)R5(q)=n0D(n)qn.\frac{1}{R^5(q)}=\sum_{n\geq 0}A(n)q^n,\qquad R^5(q)=\sum_{n\geq 0}B(n)q^n,\qquad \frac{R(q^5)}{R^5(q)}=\sum_{n\geq 0}D(n)q^n.

Conjectured sign pattern. For all integers n0n\geq0,

A(5n)<0,B(5n)<0,D(5n+1)>0.A(5n)<0,\qquad B(5n)<0,\qquad D(5n+1)>0.

An affirmative answer, together with the stated sign-pattern theorems for the other residue classes, would prove that the signs of A(n)A(n), B(n)B(n), and D(n)D(n) are periodic with period 55. The conjecture is based on numerical observation, and its status is unresolved in the supplied text.

Sources & referencesView supporting material

Primary source

Nayandeep Deka Baruah and Abhishek Sarma, “Sign Patterns and Congruences of certain infinite products involving the Rogers-Ramanujan continued fraction”, arXiv:2503.08517 (2025).

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