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 A139226 #8 Sep 27 2024 05:42:03 %S A139226 1,7,155,2667,11180715,2863245995,45812722347,768614335330822827, %T A139226 886151997189943914116283202246716075, %U A139226 63853980869412035764931125821777872829435728032869035,4388012152856549445746584486819520216982214368341183846591146667,4824670384888174809315457708695329493801178769338122219111555681805105015467 %N A139226 M(M-1)/6, where M is Mersenne prime A000668(n). %C A139226 Perfect number A000396(n) minus Mersenne prime A000668(n), divided by 3. %C A139226 Terms from a(13) on have 313 or more digits and are not listed for that reason. - _R. J. Mathar_, May 11 2008 %H A139226 Omar E. Pol, <a href="http://www.polprimos.com">Determinacion geometrica de los numeros primos y perfectos</a>. %F A139226 a(n) = A000668(n)*(A000668(n)-1)/6 = A139223(n)/6 = A139224(n)/3. %F A139226 a(n) = (A000396(n)-A000668(n))/3. %Y A139226 Cf. A000217, A000396, A000668, A036689, A139096, A139115, A139116, A139223, A139224, A139225, A139256, A139306. %K A139226 nonn %O A139226 1,2 %A A139226 _Omar E. Pol_, May 10 2008 %E A139226 More terms from _R. J. Mathar_, May 11 2008