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A083276
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Number of distinct chess positions after n plies including differences due to availability and possibility of castling and en passant captures.
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5
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1, 20, 400, 5362, 72078, 822518, 9417681, 96400068, 988187354, 9183421888, 85375278064, 726155461002
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OFFSET
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0,2
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COMMENTS
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This differs from A057745 at 6 ply and above because where an en passant capture would be illegal, the position is essentially the same as where an en passant capture is not available. It is two less than A057745 at 6 ply because the positions after 1. f4 e6/e5 2. Kf2 Qf6 3. f5 g5 are considered to be the same as after 1. f4 g5 2. Kf2 e6/e5 3. f5 Qf6.
Definition: position = position with castling and en passant information, diagram = position without castling and en passant information.
The sequence became finite on Jul 01 2014 with the introduction of a new draw rule which is automatic (the 75-move rule). - François Labelle, Apr 02 2015
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LINKS
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Tim Krabbe's chess blog, Item 283 [Mentions schachzahl1b_e.html]
Reinhard Scharnagl, Schach und Zahlen [a serious approximation to the number of possible chess positions is 2.28*10^46.]
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CROSSREFS
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KEYWORD
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hard,more,nonn,nice,fini
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AUTHOR
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EXTENSIONS
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a(11) from Peter Österlund on Feb 22 2013, verified by François Labelle on Jan 08 2017
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STATUS
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approved
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