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 A064605 #24 Jan 18 2024 02:41:28
%S A064605 1,2,8,74,146,150,158,307,526,541,16157,20289,271343,953614,1002122,
%T A064605 2233204,3015123,15988923,48033767,85110518238
%N A064605 Numbers k such that A064602(k) is divisible by k.
%C A064605 Analogous sequences for various arithmetical functions are A050226, A056650, A064605, A064606, A064607, A064610, A064611, A048290, A062982, A045345.
%C A064605 a(20) > 3*10^10. - _Donovan Johnson_, Aug 31 2012
%C A064605 a(21) > 10^11, if it exists. - _Amiram Eldar_, Jan 18 2024
%F A064605 (Sum_{j=1..k} sigma_2(j)) mod k = A064602(k) mod k = 0.
%e A064605 Summing divisor-square sums for j = 1..8 gives 1+5+10+21+26+50+50+85 = 248, which is divisible by 8, so 8 is a term and the integer quotient is 31.
%t A064605 k = 1; lst = {}; s = 0; While[k < 1000000001, s = s + DivisorSigma[2, k]; If[ Mod[s, k] == 0, AppendTo[lst, k]; Print@ k]; k++]; lst (* _Robert G. Wilson v_, Apr 25 2011 *)
%Y A064605 Cf. A001157, A064602, A050226, A056650, A064606, A064607, A064610, A064611, A064612, A048290, A062982, A045345.
%K A064605 nonn,more
%O A064605 1,2
%A A064605 _Labos Elemer_, Sep 24 2001
%E A064605 a(15)-a(19) from _Donovan Johnson_, Jun 21 2010
%E A064605 a(20) from _Amiram Eldar_, Jan 18 2024