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 A209433 #14 Feb 28 2017 02:45:47 %S A209433 1,20,400,5202,69731,766337,8708079,86540204,880526165,7996545696, %T A209433 73802185449,616052245142 %N A209433 Number of chess diagrams that can be obtained in n plies, but not in fewer plies. %C A209433 Chess diagrams are chess positions without regard to whether castling or en passant capturing is possible. The condition that the diagram cannot be obtained in fewer than n plies means that each legal chess diagram is counted exactly once in this sequence, indexed by the length of the shortest game(s) to reach it. Therefore, this sequence is finite and its sum equals the number of legal chess diagrams, estimated to be between 10^43 and 10^47. %H A209433 F. Labelle, <a href="http://wismuth.com/chess/statistics-positions.html#shortest">Statistics on chess positions</a> %H A209433 <a href="/index/Ch#chess">Index entries for sequences related to number of chess games</a> %Y A209433 Cf. A019319, A209080. %K A209433 nonn,hard,fini,more %O A209433 0,2 %A A209433 _François Labelle_, Mar 08 2012 %E A209433 a(11) from _François Labelle_, Feb 27 2017