%I A008907
%S A008907 1,3,12,38,108,174,204,153,57,15
%N A008907 Number of legal tic-tac-toe (or noughts and crosses) positions after 
               n plays, up to rotation and reflection.
%C A008907 As in chess, a "play" is an action by a single player, a "move" is two 
               contiguous plays by each opponent.
%H A008907 <a href="Sindx_Th.html#TTT">Index entries for sequences related to tic-tac-toe</
               a>
%e A008907 Example: a(2) = 12 since after 9 moves there are 15 legal positions:
%e A008907 -x- -x- -x- -x- -o- x-- x-- x-- x-o xo- o-- ox-
%e A008907 --- --- -o- o-- -x- --- --o -o- --- --- -x- ---
%e A008907 -o- o-- --- --- --- --o --- --- --- --- --- ---
%Y A008907 Sequence in context: A145951 A083215 A022727 this_sequence A048246 A129014 
               A055294
%Y A008907 Adjacent sequences: A008904 A008905 A008906 this_sequence A008908 A008909 
               A008910
%K A008907 nonn,fini,full
%O A008907 0,2
%A A008907 Russ Cox (rsc(AT)swtch.com)
%E A008907 Additional comments from David W. Wilson (davidwwilson(AT)comcast.net), 
               Jun 03 2001