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 A138877 #4 Mar 11 2014 01:34:11 %S A138877 66,2828,496496,812128,335336,858056,137328,230128,265176,191216, %T A138877 131128,144128,235976,141128,541328,108528,994776,335056,182536, %U A138877 407528,114216,598576,395336,931656,100376,811816,365456,144528,136528,131016,278128 %N A138877 Concatenation of first 3 digits and last 3 digits of n-th perfect number. %H A138877 Omar E. Pol, <a href="http://www.polprimos.com">Determinacion geometrica de los numeros primos y perfectos</a>. %H A138877 Jan Munch Pedersen, <a href="http://amicable.homepage.dk/perfect.htm">Known Perfect Numbers</a> [From Steven Bi (chenhsi(AT)stanford.edu), Jan 13 2009] %Y A138877 Cf. A000396, A104511, A138843, A138866. %K A138877 base,nonn %O A138877 1,1 %A A138877 _Omar E. Pol_, Apr 02 2008 %E A138877 Added terms 15-33 and corrected 1 term Steven Bi (chenhsi(AT)stanford.edu), Jan 13 2009