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A072461
Numbers k such that sigma(k) == 1 (mod 4).
5
1, 9, 49, 50, 81, 100, 121, 200, 338, 361, 400, 441, 450, 529, 578, 625, 676, 729, 800, 900, 961, 1089, 1156, 1352, 1600, 1682, 1800, 1849, 2209, 2312, 2401, 2450, 2704, 2738, 3042, 3200, 3249, 3362, 3364, 3481, 3600, 3969, 4050, 4225, 4489, 4624, 4761
OFFSET
1,2
LINKS
Ray Chandler, Table of n, a(n) for n = 1..10000 (first 1000 terms from Harvey P. Dale)
MATHEMATICA
Select[Range[5000], Mod[DivisorSigma[1, #], 4]==1&] (* Harvey P. Dale, Oct 24 2016 *)
PROG
(PARI) isok(n) = ((sigma(n) % 4) == 1);
CROSSREFS
Positions of 1's in A105824.
Sequence in context: A283092 A249780 A140891 * A181607 A012260 A262537
KEYWORD
nonn
AUTHOR
Labos Elemer, Jun 19 2002
EXTENSIONS
Name edited by Michel Marcus, Dec 19 2013 and Amiram Eldar, Jun 26 2024
STATUS
approved