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%I #16 Mar 30 2012 18:35:06
%S 1,3,12,38,108,174,204,153,57,15
%N Number of legal tic-tac-toe (or noughts and crosses) positions after n plays, up to rotation and reflection.
%C As in chess, a "play" is an action by a single player, a "move" is two contiguous plays by each opponent.
%H <a href="/index/Th#TTT">Index entries for sequences related to tic-tac-toe</a>
%e Example: a(2) = 12 since after 2 plays there are 12 legal positions:
%e -x- -x- -x- -x- -o- x-- x-- x-- x-o xo- o-- ox-
%e --- --- -o- o-- -x- --- --o -o- --- --- -x- ---
%e -o- o-- --- --- --- --o --- --- --- --- --- ---
%K nonn,fini,full
%O 0,2
%A _Russ Cox_
%E Additional comments from _David W. Wilson_, Jun 03 2001
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