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 A090051 #24 Mar 12 2022 22:43:20 %S A090051 1,20,400,1862,9373,51323,298821,1965313,11759158,66434263,365037821, %T A090051 1895313862 %N A090051 Number of chess diagrams that can be obtained in exactly one way in n plies. This is also the number of dual-free proof games in n plies. %C A090051 Chess diagrams are chess positions without regard to whether castling or en passant capturing is possible. They are counted in A019319. A proof game is a classic type of chess problem. %H A090051 F. Labelle, <a href="http://www.cs.berkeley.edu/~flab/chess/statistics-positions.html">Statistics on chess positions</a> %H A090051 <a href="/index/Ch#chess">Index entries for sequences related to number of chess games</a> %Y A090051 Cf. A019319, A089957, A209080. %K A090051 nonn,hard,more,nice,fini %O A090051 0,2 %A A090051 _François Labelle_, Jan 19 2004 %E A090051 a(9)-a(10) from _Arkadiusz Wesolowski_, Jan 04 2012 %E A090051 a(11) from _François Labelle_, Jan 16 2017