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 A281993 #24 Feb 11 2020 04:22:24 %S A281993 10,44,184,752,12224,49024,12580864,206158168064, %T A281993 885443715520878608384,226673591177468092350464, %U A281993 232113757366000005450563584,3894222643901120685369075227951104,1020847100762815390371677078221595082752,17126972312471518572699356075530215722269540352 %N A281993 Integers m such that sigma(m) + sigma(2*m) = 6*m. %C A281993 This is the case h = 2 of the h-perfect numbers as defined in the Harborth link. %H A281993 Heiko Harborth, <a href="http://ami.ektf.hu/uploads/papers/finalpdf/AMI_41_from57to62.pdf">On h-perfect numbers</a>, Annales Mathematicae et Informaticae, 41 (2013) pp. 57-62. %F A281993 a(n) = 2^A002235(n+1) * A007505(n+1). - _Daniel Suteu_, Feb 08 2017 [See Harborth link for a proof.] %e A281993 10 is a term since sigma(10) + sigma(20) = 60, that is 6*10. %t A281993 Select[Range[10^7], DivisorSigma[1, #] + DivisorSigma[1, 2 #] == 6 # &] (* _Michael De Vlieger_, Feb 04 2017 *) %o A281993 (PARI) isok(n, h=2) = sigma(n) + sigma(h*n) == 2*n*(h+1); %Y A281993 Cf. A000203, A097215. %K A281993 nonn %O A281993 1,1 %A A281993 _Michel Marcus_, Feb 04 2017 %E A281993 More terms from _Jinyuan Wang_, Feb 11 2020