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%I #12 Jun 22 2019 09:21:41
%S 6,12,28,70,88,108,168,220,348,496,550,580,726,748,798,910,918,952,
%T 1032,1120,1200,1240,1504,1644,1672,1840,1888,2140,2205,2392,2470,
%U 2472,2814,3190,3222,3580,3804,4030,4648,4732,4758,5032,5670,5830
%N Values of n such that sigma(n)-2n (the abundance of n) is a (nonnegative) square.
%H Amiram Eldar, <a href="/A109510/b109510.txt">Table of n, a(n) for n = 1..10000</a>
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/Abundance.html">Abundance</a>
%e 12 is in the sequence since sigma(12) - 2*12 = 28 - 24 = 4 = 2^2 is a square.
%t Select[Range[6000], IntegerQ@Sqrt[DivisorSigma[1, #] - 2 #] &] (* _Amiram Eldar_, Jun 22 2019 *)
%o (PARI) isok(n) = issquare(sigma(n) - 2*n); \\ _Michel Marcus_, Jun 22 2019
%Y Cf. A000203, A000290, A023196, A033880.
%Y Cf. A000396 (perfect numbers: a subsequence).
%K nonn
%O 1,1
%A _Eric W. Weisstein_, Jun 30 2005
%E Name clarified by _Amiram Eldar_, Jun 22 2019
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