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A227303 Numbers k such that k divides sigma(3*k). 4
1, 2, 4, 28, 40, 78, 90, 224, 360, 496, 546, 2016, 2184, 8128, 10080, 10920, 11880, 66528, 145236, 174592, 714240, 726180, 1571328, 4333056, 6168960, 7856640, 12065760, 15177600, 33550336, 47663616, 69521760, 80196480, 91963648, 99993600, 156854880, 459818240, 492101632 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
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
LINKS
MATHEMATICA
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 *)
PROG
(PARI) isok(k) = !(sigma(3*k) % k); \\ Michel Marcus, Mar 07 2021
CROSSREFS
Sequence in context: A226347 A305738 A323447 * A066228 A110881 A156449
KEYWORD
nonn
AUTHOR
Alex Ratushnyak, Jul 05 2013
STATUS
approved

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Last modified June 19 06:59 EDT 2024. Contains 373492 sequences. (Running on oeis4.)