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%I #17 Apr 05 2024 08:17:12
%S 25,169,225,289,841,1225,1369,1521,1681,2025,2601,2809,3025,3721,5329,
%T 7569,7921,8281,9025,9409,10201,11025,11881,12321,12769,13225,13689,
%U 14161,15129,15625,18225,18769,20449,22201,23409,24025,24649,25281,27225,29929,32761,33489,34969,37249,38809,41209,46225,47961,52441,54289,55225
%N Odd numbers k for which sigma(k) == 3 (mod 4).
%C These are all squares. Square roots are in A324909.
%H Antti Karttunen, <a href="/A324899/b324899.txt">Table of n, a(n) for n = 1..10000</a>
%H <a href="/index/Si#SIGMAN">Index entries for sequences related to sigma(n)</a>.
%F a(n) = A324909(n)^2. - _Amiram Eldar_, Apr 05 2024
%t Select[Range[1, 235, 2]^2, Mod[DivisorSigma[1, #], 4] == 3 &] (* _Amiram Eldar_, Apr 05 2024 *)
%o (PARI) isA324899(n) = ((n%2)&&3==(sigma(n)%4));
%Y Intersection of A016754 and A072462.
%Y Cf. A000203, A324909 (square roots).
%Y Cf. A325311 (a subsequence).
%K nonn
%O 1,1
%A _Antti Karttunen_, Apr 20 2019
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