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A232354
Numbers k that divide sigma(k^2) where sigma is the sum of divisors function (A000203).
4
1, 39, 793, 2379, 7137, 13167, 76921, 78507, 230763, 238887, 549549, 692289, 863577, 1491633, 1672209, 2076867, 4317885, 7615179, 8329831, 10441431, 23402223, 24989493, 37776123, 53306253, 53695813, 55871145, 74968479, 83766969, 133854435, 144688401, 161087439, 189437391
OFFSET
1,2
COMMENTS
Squarefree terms are: 1, 39, 793, 2379, 76921, 230763, 8329831, 24989493, 53695813, 161087439, ... Quotients are: 1, 61, 873, 3783, 11737, 26543, 85563, 141911, 370773, 417263, 1155561, ... - Michel Marcus, Nov 23 2013
Many terms are also in sequence A069520, cf. A232067 for the intersection of these two sequences. - M. F. Hasler, Nov 24 2013
LINKS
Jose Arnaldo Bebita Dris, A new approach to odd perfect numbers via GCDs, arXiv:2202.08116 [math.NT], 2022.
FORMULA
A065764(a(n)) mod a(n) = 0.
MATHEMATICA
Select[Range[10^5], Divisible[DivisorSigma[1, #^2], #] &] (* Alonso del Arte, Dec 06 2013 *)
PROG
(PARI) isok(n) = (sigma(n^2) % n) == 0; \\ Michel Marcus, Nov 23 2013
KEYWORD
nonn
AUTHOR
Alex Ratushnyak, Nov 22 2013
STATUS
approved