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 A385810 #14 Jul 13 2025 23:57:41 %S A385810 4,6,28,45,48,60,156,208,360,496,1170,2016,2520,2925,5733,7605,8128, %T A385810 166617,167580,380160,659044,964080,1085760,1539900,1571328,1693440, %U A385810 1778400,2069613,2224800,2306304,2410200,2502720,2522880,4242420,4311216,4840192,4917744,4961484,5331744,5761536 %N A385810 Integers x such that sigma(x)^2 - 3*x^2 is a square. %H A385810 S. I. Dimitrov, <a href="https://arxiv.org/abs/2408.07387">Generalizations of amicable numbers</a>, arXiv:2408.07387 [math.NT], 2024. %t A385810 fQ[x_] := IntegerQ@ Sqrt[DivisorSigma[1, x]^2 - 3*x^2]; Select[Range[2^16], fQ] (* _Michael De Vlieger_, Jul 09 2025 *) %o A385810 (PARI) isok(x) = issquare(sigma(x)^2-3*x^2); %Y A385810 Subsequence, with (x,x,x) triples, of A385531. %Y A385810 Cf. A000203. %Y A385810 Supersequence of A000396. %K A385810 nonn %O A385810 1,1 %A A385810 _Michel Marcus_, Jul 09 2025