Existence of a composite n ≠ 4 with φ⁺(n) dividing n−1
Determine whether there exists any positive composite integer n other than n=4 such that φ⁺(n) divides n−1, where φ⁺(n)=∏_{p\mid n}(φ(p^{v_p(n)})+1) and φ(·) is Euler’s totient function.
References
Open question 4: Is there any positive composite integer $n\neq 4$ such that $\varphi+(n)\mid (n-1)$?
— Divisibility and Sequence Properties of $σ^+$ and $\varphi^+$
(2508.11660 - Mandal, 6 Aug 2025) in Section 2, Main Results (Open question 4)