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On the number of divisors of Mersenne numbers
Vjekoslav Kova\v{c}, Florian Luca
https://arxiv.org/abs/2506.04883 https://arxiv.org/pd…

On the number of divisors of Mersenne numbers
Denote $f(n):=\sum_{1\le k\le n} τ(2^k-1)$, where $τ$ is the number of divisors function. Motivated by a question of Paul Erdős, we show that the sequence of ratios $f(2n)/f(n)$ is unbounded. We also present conditional results on the divergence of this sequence to infinity. Finally, we test numerically both the conjecture $f(2n)/f(n)\to\infty$ and our sufficient conditions for it to hold.