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 A382504 #50 Apr 08 2025 22:03:19 %S A382504 6,10,25,28,496,652,8128,10682,10828,33550336,44655764,8589869056, %T A382504 8623554304 %N A382504 Numbers k such that one or both of sigma(k) + k and sigma(k) - k is a perfect number. %C A382504 10 and 838476969534191044 are the only known numbers k for which sigma(k) + k is a perfect number. %H A382504 Leo Hennig, <a href="https://groups.google.com/g/seqfan/c/AWt75irA3TY">One entry and just one entry</a>, Seqfan thread. %e A382504 sigma(6) = 12 and 12 - 6 = 6. %e A382504 sigma(10) = 18 and 18 + 10 = 28. %e A382504 sigma(25) = 31 and 31 - 25 = 6. %o A382504 (PARI) isp(x) = if (x>0, sigma(x) == 2*x); %o A382504 isok(x) = isp(sigma(x)-x) || isp(sigma(x)+x); \\ _Michel Marcus_, Mar 29 2025 %Y A382504 Supersequence of A000396 and of A237286. %Y A382504 Cf. A000203. %K A382504 nonn,more %O A382504 1,1 %A A382504 _Leo Hennig_, Mar 29 2025