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Search: id:A008907
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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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+0
4
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OFFSET
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0,2
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COMMENT
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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
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Index entries for sequences related to tic-tac-toe
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EXAMPLE
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Example: a(2) = 12 since after 9 moves there are 15 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
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Sequence in context: A145951 A083215 A022727 this_sequence A048246 A129014 A055294
Adjacent sequences: A008904 A008905 A008906 this_sequence A008908 A008909 A008910
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KEYWORD
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nonn,fini,full
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AUTHOR
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Russ Cox (rsc(AT)swtch.com)
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EXTENSIONS
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Additional comments from David W. Wilson (davidwwilson(AT)comcast.net), Jun 03 2001
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