This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A109510 #13 Feb 16 2025 08:32:58 %S A109510 6,12,28,70,88,108,168,220,348,496,550,580,726,748,798,910,918,952, %T A109510 1032,1120,1200,1240,1504,1644,1672,1840,1888,2140,2205,2392,2470, %U A109510 2472,2814,3190,3222,3580,3804,4030,4648,4732,4758,5032,5670,5830 %N A109510 Values of n such that sigma(n)-2n (the abundance of n) is a (nonnegative) square. %H A109510 Amiram Eldar, <a href="/A109510/b109510.txt">Table of n, a(n) for n = 1..10000</a> %H A109510 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Abundance.html">Abundance</a> %e A109510 12 is in the sequence since sigma(12) - 2*12 = 28 - 24 = 4 = 2^2 is a square. %t A109510 Select[Range[6000], IntegerQ@Sqrt[DivisorSigma[1, #] - 2 #] &] (* _Amiram Eldar_, Jun 22 2019 *) %o A109510 (PARI) isok(n) = issquare(sigma(n) - 2*n); \\ _Michel Marcus_, Jun 22 2019 %Y A109510 Cf. A000203, A000290, A023196, A033880. %Y A109510 Cf. A000396 (perfect numbers: a subsequence). %K A109510 nonn %O A109510 1,1 %A A109510 _Eric W. Weisstein_, Jun 30 2005 %E A109510 Name clarified by _Amiram Eldar_, Jun 22 2019