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 A213439 N1106 #6 Jun 11 2012 22:02:33 %S A213439 1,3,8,25,72,231,696,2268,7030,23155,73188,242957,778946,2601345, %T A213439 8430992,28289598,92470194,311472985,1025114180,3463982109, %U A213439 11465054942,38846071490,129180293184,438697998100,1464716085664,4984101484479,16698145444260,56918978668875 %N A213439 A000136(n)/2. %D A213439 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence). %Y A213439 Cf. A000136, A000560. %K A213439 nonn %O A213439 2,2 %A A213439 _N. J. A. Sloane_, Jun 11 2012