A391012 Numbers k such that 2*k and k + 2 have same sum of divisors.

2, 4678, 26206, 54178, 230578, 467458, 474238, 4532638, 4682998, 5761978, 20427262, 20568598, 23468398, 28119418, 34385818, 36447838, 74158918, 79065502, 87558838, 98048518, 109444498, 113149438, 148380958, 164401378, 175556638, 187270198, 193156738, 219160078, 224488738

Offset

1,1

Comments

Numbers k for which sigma(2*k) = sigma(k + 2) where sigma = A000203.

Links

Table of n, a(n) for n=1..29.

Example

4678 is a term because A000203(2*4678) = A000203(4678 + 2) = 16380.

Mathematica

q[k_] := Equal @@ DivisorSigma[1, {k + 2, 2*k}]; Select[Range[5*10^5], q] (* Amiram Eldar, Jan 27 2026 *)

Prog

(Magma) [k: k in [1..474238] | SumOfDivisors(2*k) eq SumOfDivisors(k + 2)];

Crossrefs

Cf. A000203, A002961.

Sequence in context: A292391 A195002 A203756 * A232712 A262059 A153737

Adjacent sequences: A391009 A391010 A391011 * A391013 A391014 A391015

Keyword

nonn

Author

Juri-Stepan Gerasimov, Jan 26 2026

Extensions

More terms from Amiram Eldar, Jan 27 2026

Status

approved