Existence of a composite n with n+1 dividing σ⁺(n)
Ascertain whether there exists any positive composite integer n such that n+1 divides σ⁺(n), where σ⁺(n)=∏_{p\mid n}(σ(p^{v_p(n)})+1), σ(·) is the sum-of-divisors function, and v_p(n) is the highest power of the prime p dividing n.
References
Open question 2: Is there any positive composite integer $n$ such that $n+1\mid \sigma+(n)$?
— Divisibility and Sequence Properties of $σ^+$ and $\varphi^+$
(2508.11660 - Mandal, 6 Aug 2025) in Section 2, Main Results (Open question 2)