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 A139223 #11 Sep 27 2024 05:41:39 %S A139223 6,42,930,16002,67084290,17179475970,274876334082,4611686011984936962, %T A139223 5316911983139663484697699213480296450, %U A139223 383123885216472214589586754930667236976614368197214210 %N A139223 M*(M-1), where M is Mersenne prime A000668(n). %H A139223 Omar E. Pol, <a href="http://www.polprimos.com">Determinacion geometrica de los numeros primos y perfectos</a>. %F A139223 a(n) = A000668(n)*(A000668(n)-1). %Y A139223 Cf. A000668, A036689, A139115, A139116, A139224, A139225, A139226, A139256. %K A139223 nonn %O A139223 1,1 %A A139223 _Omar E. Pol_, May 10 2008 %E A139223 More terms from _R. J. Mathar_, Jun 24 2009