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 A172050 #2 Mar 30 2012 18:53:09 %S A172050 0,4,8,13,20,30,46,72,116,191,320,542,924,1580,2704,4625,7900,13470, %T A172050 22922,38928,65980,111619,188488,317758,534840,898900,1508696,2528917, %U A172050 4233956,7080606,11828710,19741272,32916164,54835655,91276304 %N A172050 A008585+A029907. %Y A172050 Cf. A008585, A029907, (1-((-1)^a(n+4)))/2 = A172051. %K A172050 nonn %O A172050 0,2 %A A172050 _Mats Granvik_, Jan 24 2010