%I A090051
%S A090051 1,20,400,1862,9373,51323,298821,1965313,11759158
%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="Sindx_Ch.html#chess">Index entries for sequences related to 
               number of chess games</a>
%Y A090051 Cf. A019319, A089957.
%Y A090051 Sequence in context: A063815 A158534 A075843 this_sequence A089957 A019319 
               A083276
%Y A090051 Adjacent sequences: A090048 A090049 A090050 this_sequence A090052 A090053 
               A090054
%K A090051 nonn,hard,nice
%O A090051 0,2
%A A090051 Francois Labelle (flab(AT)cs.berkeley.edu), Jan 19 2004