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 A138728 #6 Mar 11 2014 01:34:11 %S A138728 2,3,6,4,7,28,16,31,496,64,127,8128,4096,8191,33550336,65536,131071, %T A138728 8589869056,262144,524287,137438691328,1073741824,2147483647, %U A138728 2305843008139952128,1152921504606846976,2305843009213693951 %N A138728 Array read by rows: row n lists n-th even superperfect number A061652(n), n-th Mersenne prime A000668(n) and n-th perfect number A000396(n). %H A138728 L. C. Noll, <a href="http://isthe.com/chongo/tech/math/prime/mersenne.html">Mersenne Prime Digits and Names</a>. %H A138728 J. M. Pedersen, <a href="http://amicable.homepage.dk/perfect.htm">Known Perfect Numbers</a>. %H A138728 Omar E. Pol, <a href="http://www.polprimos.com">Determinacion geometrica de los numeros primos y perfectos</a>. %e A138728 Array begins: %e A138728 2, 3, 6 %e A138728 4, 7, 28 %e A138728 16, 31, 496 %Y A138728 Cf. A000396, A000668, A019279, A061652, A138818, A138819. %K A138728 nonn,tabf %O A138728 1,1 %A A138728 _Omar E. Pol_, Apr 07 2008