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%I #24 Mar 12 2022 22:43:20
%S 1,20,400,1862,9373,51323,298821,1965313,11759158,66434263,365037821,
%T 1895313862
%N 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 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 F. Labelle, <a href="http://www.cs.berkeley.edu/~flab/chess/statistics-positions.html">Statistics on chess positions</a>
%H <a href="/index/Ch#chess">Index entries for sequences related to number of chess games</a>
%Y Cf. A019319, A089957, A209080.
%K nonn,hard,more,nice,fini
%O 0,2
%A _François Labelle_, Jan 19 2004
%E a(9)-a(10) from _Arkadiusz Wesolowski_, Jan 04 2012
%E a(11) from _François Labelle_, Jan 16 2017
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