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 A272716 #6 May 10 2016 00:08:28 %S A272716 440,28109312,79228362752 %N A272716 Numbers equal to the sum of their proper divisors d such that d mod 3 = 1. %C A272716 10^11 < a(4) <= 8581256320000. %C A272716 The numbers equal to the sum of their proper divisors which are a multiple of 3 are the perfect numbers (A000396) multiplied by 3. %e A272716 The proper divisors of 440 which are congruent to 1 mod 3 are 1, 4, 10, 22, 40, 55, 88, and 220. Since their sum is 440, 440 is a term. %t A272716 Select[Range[5000], # == Plus @@ Select[Most@ Divisors@#, Mod[#,3] == 1 &] &] %o A272716 (PARI) is(n)=sumdiv(n,d,if(d%3==1,d,0))==if(n%3==1,2*n,n) \\ _Charles R Greathouse IV_, May 09 2016 %Y A272716 Cf. A272715, A000396. %K A272716 nonn,bref,more,hard %O A272716 1,1 %A A272716 _Giovanni Resta_, May 05 2016