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A227303 Numbers k such that k divides sigma(3*k). 4

%I #26 Oct 14 2023 00:07:09

%S 1,2,4,28,40,78,90,224,360,496,546,2016,2184,8128,10080,10920,11880,

%T 66528,145236,174592,714240,726180,1571328,4333056,6168960,7856640,

%U 12065760,15177600,33550336,47663616,69521760,80196480,91963648,99993600,156854880,459818240,492101632

%N Numbers k such that k divides sigma(3*k).

%C If k belongs to the sequence, then sigma(3*k)/k is an integer, so sigma(3*k)/(3*k) is either an integer or a third of an integer, so 3*k is either multiperfect or belongs to A160320 or A160321. - _Michel Marcus_, Jul 09 2013

%H Jud McCranie, <a href="/A227303/b227303.txt">Table of n, a(n) for n = 1..65</a>

%t k = 0; lst = {}; While[k < 10^11, If[ Mod[ DivisorSigma[1, 3 k], k] == 0, AppendTo[lst, k]]; k++]; lst (* _Robert G. Wilson v_, Mar 07 2021 *)

%o (PARI) isok(k) = !(sigma(3*k) % k); \\ _Michel Marcus_, Mar 07 2021

%Y Cf. A000203, A007691, A227302.

%Y Cf. A160320, A160321.

%K nonn

%O 1,2

%A _Alex Ratushnyak_, Jul 05 2013

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Last modified March 28 10:55 EDT 2024. Contains 371241 sequences. (Running on oeis4.)