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 A253087 #13 Jun 09 2016 03:10:14 %S A253087 1,4,12,48,144,440,1816,6816,25816,101856,397944,1573464,6274560, %T A253087 25071152,100180872,400625360 %N A253087 a(n) = A253086(2^n-1). %C A253087 In trying to understand A253086, this subsequence looked like the best place to attack it. But there is unfortunately no obvious formula even here. %H A253087 <a href="/index/Ce#cell">Index entries for sequences related to cellular automata</a> %Y A253087 Cf. A253086. %K A253087 nonn,more %O A253087 0,2 %A A253087 _N. J. A. Sloane_, Feb 12 2015 %E A253087 a(10)-a(15) from _Lars Blomberg_, Jun 09 2016