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 A271858 #9 Apr 17 2016 09:32:26 %S A271858 0,1,1,2,5,20,56,276,2136,13756,148352,2727448,41044816,1056334024, %T A271858 46033137324 %N A271858 Number of ways to trisect a triangle with side length n exactly into three identical parts in a triangular lattice. %C A271858 In the case that n is not divisible by 3 the central triangle is removed, otherwise the dissection would not be possible. %H A271858 G. P. Jelliss, <a href="http://www.mayhematics.com/j/gpj22.htm#(2)">Trisected Triangles</a>, The Games and Puzzles Journal, Issue 22, January-April 2002. %Y A271858 Cf. A268606, A271857, A113900, A257952. %K A271858 nonn,more %O A271858 1,4 %A A271858 _Andrew Howroyd_, Apr 15 2016