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 A227904 #21 Jan 10 2022 22:24:15
%S A227904 1,2,39,78,100,126,434,501,1313,54111,359466,523219,6601441,8034674,
%T A227904 54092207,64149290,158882288,3016740661,20951813922,52815759197,
%U A227904 120508871819
%N A227904 Numbers k such that Sum_{j=1..k} antisigma(j) == 0 (mod sigma(k)).
%C A227904 Tested up to k = 10^6.
%C A227904 a(22) > 2.1774*10^11. - _Kevin P. Thompson_, Jan 10 2022
%e A227904 Sum_{j=1..39} antisigma(j) = 9408, sigma(39) = 56 and 9408 mod 56 = 0, so 39 is a term.
%p A227904 with(numtheory); P:=proc(q) local a, n; a:=0;
%p A227904 for n from 3 to q do a:=a+n*(n+1)/2-sigma(n);
%p A227904 if (a mod sigma(n))=0 then print(n); fi; od; end: P(10^9);
%Y A227904 Cf. A000203, A024816, A076664, A168127.
%K A227904 nonn,more
%O A227904 1,2
%A A227904 _Paolo P. Lava_, Oct 15 2013
%E A227904 a(13)-a(17) from _Donovan Johnson_, Oct 15 2013
%E A227904 a(18)-a(21) from _Kevin P. Thompson_, Jan 10 2022