Recently, Andrews and El Bachraoui studied a partition function $s_1(n)$, which counts the number of two-color partitions into distinct parts of $n$ whose smallest part occurs in one prescribed color only, while every larger part may occur in either color or in both colors. They obtained a complete description modulo 4 for $s_1(n)$. They also considered a $q$-series $T_{o}(q)$ which is the odd companion series of the generating function for $s_1(n)$. At the end of their paper, they presented a conjecture on the parity of the coefficients of $T_o(q)$. In this paper, we confirm this conjecture. Moreover, we establish an infinite family of congruences modulo 8 for the coefficients of $S_1(q)$ and prove that the set of integers satisfying $s_1(n)\equiv 0\pmod 8$ has natural density one.
Andrews and Bachraoui (\textit{Int. J. Number Theory} (2026)) studied the two-color partition function $F(n)$ of a non-negative integer $n$ wherein odd parts may appear in two colors (red and blue) and even parts appear in one color (blue). For any non-negative integer $n,$ they also considered some restricted versions of $F(n)$: $F_0(n)$: the number of partitions of $n$ counted by $F(n)$ such that the number of odd parts in red color is even; $F_1(n)$: the number of partitions counted by $F(n)$ such that the number of odd parts in red color is odd; $H(n)$: the number of partitions of $n$ counted by $F(n)$ such that the parts of the same color do not repeat. The main purpose of this paper is to present the analytic proofs of the $q$-series identities connected with $F(n)$ and $H(n),$ which appeared as open problems in the original paper. We also prove some congruences of $F_0(n)$ and $F_1(n)$ modulo $2,$ $4,$ and $8$ by using $ q $-series.
In this paper, we prove a conjecture of Andrews and El Bachraoui concerning the parity of certain two-color partitions. Precisely, we show that if the Fourier coefficient $t_o(n)$ of the corresponding $q$-series is odd, then $8n+9$ is represented by the binary quadratic form $x^2+2y^2$.
In this paper, we prove an exceptional sign pair phenomenon for three $q$-series from Ramanujan's Lost Notebook, namely $v_2(q),v_3(q)$, and $v_4(q)$. This was first observed by Andrews in a 1986 paper. Building on the recent work of Kundu, Storzer, Wang, and the author, which established that the coefficients of these $q$-series are alternating in sign except in a density-zero set, we study the exceptional indices where the alternating sign pattern fails. We prove that these exceptional indices occur infinitely often in a structured manner. More precisely, we show that there exist infinitely many pairs of consecutive coefficients having the same sign, and that at least one coefficient in each pair is a local minimum of the sequence of absolute values of the coefficients. Our proof combines precise asymptotic expansions for the coefficients with a careful analysis of an oscillatory factor appearing in the expansions which governs the exceptional sign behavior.
Let $a(n)$ be the sequence A028342 in the On-Line Encyclopedia of Integer Sequences (OEIS), defined by the exponential generating function $\sum_{n\ge0} a(n)x^n/n! = \prod_{i\ge1}(1-x^i)^{-1/i}$. Equivalently, $a(n)$ counts permutations of an $n$-element labeled set in which every cycle is assigned one divisor of its length, where a cycle of length $m$ has $d(m)$ choices, $d(m)$ being the number of positive divisors of $m$. We prove a family of congruences for $a$, conjectured by Peter Bala. They state that $k \mid a(n+k)+a(n)$ for odd $k$, that $k \mid a(n+k)-a(n)$ for $k\equiv 0,2,6 \pmod 8$, and that $k \mid 2(a(n+k)-a(n))$ for $k\equiv 4\pmod 8$. The proof first establishes a product congruence $a(n+k)\equiv a(n)a(k)\pmod k$, and then computes $a(p^r)\bmod p^r$ for each prime power by counting the colored permutations fixed by a subgroup of order $p$.
Let $K/k$ be a finite abelian extension of number fields with Galois group $G$ and let $n\geq 2$. We prove, assuming the relevant $p$-part of the equivariant Tamagawa number conjecture, first-derivative analogues of the Deligne-Ribet integrality theorem and of the Coates-Sinnott conjecture. We construct a rank-one leading term from the first derivatives at $s=1-n$ of the $S$-truncated Artin $L$-functions and show that it satisfies an integral annihilation property. We then attach to this leading term a fractional ideal of $\mathbb Q_p[G]$ and prove that, up to the natural torsion factor coming from $K_{2n-1}(O_K)$, this ideal annihilates the even $K$-group $K_{2n-2}(O_{K,S})$. The proof uses determinant methods, $\Sigma$-modified \'etale complexes, and a cancellation argument which removes the auxiliary Euler factors.
Stone (Ph.D.\ thesis, Department of Operations Research, Stanford University, 1981) proved that every matrix in $U \cap Q_0$ is a $P_0$-matrix and conjectured that the same conclusion holds for the larger class $E_0^f \cap Q_0$ of fully semimonotone $Q_0$-matrices. Murthy and Parthasarathy [SIAM J.\ Matrix Anal.\ Appl.\ 16 (1995), 1268--1286] verified the conjecture for matrices of order up to $4 \times 4$, for $5 \times 5$ and $6 \times 6$ matrices under additional hypotheses, and for several special subclasses of arbitrary order, but the conjecture remains open in general. In this paper we prove that every $E_0^f$-matrix with positive determinant is a $P_0$-matrix, for matrices of arbitrary order $n$; our proof proceeds by induction on $n$, via an algebraic analysis of principal minors under principal pivotal transforms. We further exhibit a matrix $A \in E_0^f$ with $\det A>0$ that fails to belong to $Q_0$, showing that the hypothesis $\det A>0$ used in our theorem cannot, by itself, be deduced from membership in $Q_0$, and hence does not on its own yield a proof of Stone's conjecture. Stone's conjecture itself remains open.