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%I #11 Feb 20 2020 09:31:43
%S 1,9,49,50,81,100,121,200,338,361,400,441,450,529,578,625,676,729,800,
%T 900,961,1089,1156,1352,1600,1682,1800,1849,2209,2312,2401,2450,2704,
%U 2738,3042,3200,3249,3362,3364,3481,3600,3969,4050,4225,4489,4624,4761
%N Sigma(n) == 1 mod 4.
%H Ray Chandler, <a href="/A072461/b072461.txt">Table of n, a(n) for n = 1..10000</a> (first 1000 terms from Harvey P. Dale)
%t Select[Range[5000],Mod[DivisorSigma[1,#],4]==1&] (* _Harvey P. Dale_, Oct 24 2016 *)
%o (PARI) isok(n) = ((sigma(n) % 4) == 1);
%Y Cf. A000203, A028982, A072462.
%K nonn
%O 1,2
%A _Labos Elemer_, Jun 19 2002
%E Name edited by _Michel Marcus_, Dec 19 2013
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