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A032522
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Number of symmetric solutions to non-attacking queens problem on n X n board.
(Formerly M0330 N0125)
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6
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1, 0, 0, 2, 2, 4, 8, 4, 16, 12, 48, 80, 136, 420, 1240, 3000, 8152, 18104, 44184, 144620, 375664, 1250692, 3581240, 11675080, 34132592, 115718268, 320403024, 1250901440, 3600075088, 14589438024, 43266334696, 181254386312
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,4
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REFERENCES
| N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
R. J. Walker, An enumerative technique for a class of combinatorial problems, pp. 91-94 of Proc. Sympos. Applied Math., vol. 10, Amer. Math. Soc., 1960.
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LINKS
| W. Schubert, N-Queens page
M. Szabo, Non-attacking Queens Problem Page
W. Schubert, Table of n, a(n) for n = 1..39
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CROSSREFS
| Cf. A002562, A033148, A037224, A037223.
Sequence in context: A116694 A137778 A000017 * A077964 A077968 A123958
Adjacent sequences: A032519 A032520 A032521 * A032523 A032524 A032525
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KEYWORD
| nonn,nice,hard
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AUTHOR
| Miklos SZABO (mike(AT)ludens.elte.hu)
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EXTENSIONS
| More terms for n = 33..36 from W. Schubert (wschubnq(AT)gmx.de), Jul 31 2009
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