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 A272715 #10 May 11 2016 16:23:53 %S A272715 280,34960,4960000,15887872,20527600,105056320,44781248512 %N A272715 Numbers equal to the sum of their proper divisors d such that d mod 3 = 2. %C A272715 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 A272715 The proper divisors of 280 which are congruent to 2 mod 3 are 2, 5, 8, 14, 20, 35, 56, and 140. Since their sum is 280, 280 is a term. %t A272715 Select[Range[40000], # == Plus @@ Select[ Most@ Divisors[#], Mod[#, 3] == 2 &] &] %o A272715 (PARI) is(n)=sumdiv(n, d, if(d%3==2, d, 0))==if(n%3==2, 2*n, n) \\ _Charles R Greathouse IV_, May 09 2016 %Y A272715 Cf. A272716, A000396, A078182 (sum of proper and improver divisors). %K A272715 nonn,more %O A272715 1,1 %A A272715 _Giovanni Resta_, May 05 2016