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This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

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A209080 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.

Original entry on oeis.org

1, 20, 400, 1702, 8659, 49401, 287740, 1934794, 11569093, 65443733, 360231372, 1872156836
Offset: 0

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Author

François Labelle, Mar 04 2012

Keywords

Comments

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.

Links

Crossrefs

Cf. A019319, A090051, A209433.

Extensions

a(11) from François Labelle, Feb 27 2017
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Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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