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A008907
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Number of legal tic-tac-toe (or noughts and crosses) positions after n plays, up to rotation and reflection.
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3
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OFFSET
| 0,2
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COMMENTS
| As in chess, a "play" is an action by a single player, a "move" is two contiguous plays by each opponent.
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LINKS
| Index entries for sequences related to tic-tac-toe
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EXAMPLE
| Example: a(2) = 12 since after 2 plays there are 12 legal positions:
-x- -x- -x- -x- -o- x-- x-- x-- x-o xo- o-- ox-
--- --- -o- o-- -x- --- --o -o- --- --- -x- ---
-o- o-- --- --- --- --o --- --- --- --- --- ---
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CROSSREFS
| Sequence in context: A145951 A083215 A022727 * A048246 A129014 A055294
Adjacent sequences: A008904 A008905 A008906 * A008908 A008909 A008910
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KEYWORD
| nonn,fini,full
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AUTHOR
| Russ Cox (rsc(AT)swtch.com)
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EXTENSIONS
| Additional comments from David W. Wilson (davidwwilson(AT)comcast.net), Jun 03 2001
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