Universal odd-prime valuation bound for the sum of divisors

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Let p>2p>2 be a fixed prime, and let n∈Nn\in\mathbb{N}. Write σ(n)\sigma(n) for the sum of the positive divisors of nn, and let νp\nu_p denote the pp-adic valuation. For a prime q∣nq\mid n, write νq(n)\nu_q(n) for the exponent of qq in nn. The relevant conditions are: (1) every prime qq dividing nn satisfies νp(σ(qνq(n)))≤⌊log⁡p(qνq(n))⌋\nu_p(\sigma(q^{\nu_q(n)}))\leq\lfloor\log_p(q^{\nu_q(n)})\rfloor; or (2) every prime qq dividing nn that satisfies νp(σ(qνq(n)))=⌈log⁡p(qνq(n))⌉\nu_p(\sigma(q^{\nu_q(n)}))=\lceil\log_p(q^{\nu_q(n)})\rceil is less than pp.

Universal odd-prime valuation conjecture. Every n∈Nn\in\mathbb{N} satisfies condition (1) or (2). Consequently,

up(σ(n))≤⌈log⁡pn⌉.u_p(\sigma(n))\leq\lceil\log_p n\rceil.

A complete characterization of the indices nn for which equality holds in this bound remains open, although the bound is proved under the stated conditions.

References

Primary source

Tewodros Amdeberhan, Victor H. Moll, Vaishavi Sharma and Diego Villamizar, “Arithmetic properties of the sum of divisors”, arXiv:2007.03088 (2020).

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