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 A139224 #9 Sep 27 2024 05:41:51 %S A139224 3,21,465,8001,33542145,8589737985,137438167041,2305843005992468481, %T A139224 2658455991569831742348849606740148225, %U A139224 191561942608236107294793377465333618488307184098607105 %N A139224 M(M-1)/2, where M is Mersenne prime A000668(n). %C A139224 Perfect number A000396(n) minus Mersenne prime A000668(n). %H A139224 Omar E. Pol, <a href="http://www.polprimos.com">Determinacion geometrica de los numeros primos y perfectos</a>. %F A139224 a(n) = A000668(n)*(A000668(n)-1)/2. %F A139224 a(n) = A000396(n)-A000668(n). %Y A139224 Cf. A000217, A000396, A000668, A036689, A139096, A139115, A139116, A139223, A139225, A139226, A139256, A139306. %K A139224 nonn %O A139224 1,1 %A A139224 _Omar E. Pol_, May 10 2008 %E A139224 More terms from _Max Alekseyev_, Mar 09 2009