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A209080
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Number of chess diagrams that can be obtained in exactly one way in n plies and cannot be obtained in fewer plies. This is also the number of dual-free shortest proof games in n plies.
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2
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1, 20, 400, 1702, 8659, 49401, 287740, 1934794, 11569093, 65443733, 360231372, 1872156836
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OFFSET
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0,2
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COMMENTS
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Chess diagrams are chess positions without regard to whether castling or en passant capturing is possible. They are counted in A019319. A shortest proof game (SPG) is a classic type of chess problem. Most published SPGs are dual-free (have only one solution), which is why we count diagrams that are obtained in exactly one way in the minimum number of plies.
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CROSSREFS
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KEYWORD
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nonn,hard,fini,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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