Merca's conjecture on divisibility of divisor sums in arithmetic progressions

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For an integer k≥0k\geq0, let

σ0(n)=∑d∣n1\sigma_0(n)=\sum_{d\mid n}1

denote the number of positive divisors of nn. Merca's conjecture. If

σ0(An+B)≡0  (mod  2k)\sigma_0(An+B)\equiv0\,\,({\rm mod}\,\,{2^k})

for every n≥0n\geq0, then there is a sequence of prime numbers p1≤p2≤⋯≤pk−1p_1\leq p_2\leq\cdots\leq p_{k-1} such that (p1p2⋯pk−1)2(p_1p_2\cdots p_{k-1})^2 divides AA and p1p2⋯pk−1p_1p_2\cdots p_{k-1} divides BB. This question is described in the source as too broad to be meaningfully resolved explicitly in this form.

References

Primary source

William Craig and Mircea Merca, “On Ramanujan-type Congruences for Multiplicative Functions”, arXiv:2112.05649 (2022).

Additional references

2 papers in this index state this conjecture (2014–2021). The statement above is taken from the most recent of them; the others are arXiv:1405.4755.

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