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A005650
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Number of "magic squares" of order n (see comment line for exact definition).
(Formerly M2704)
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1
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1, 1, 3, 7, 47, 207, 2249, 14501, 216273, 1830449, 34662523, 362983263, 8330310559, 103938238111, 2801976629841, 40574514114061, 1256354802202337, 20708839411614753, 724160187180691379, 13386284447024070647
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,3
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COMMENTS
| This is the number of n X n square arrays with nonnegative integer entries in which every row and column add to 2 (A000681) normalized by dividing by n!/2^[n/2].
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REFERENCES
| L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 125, #25, A_n.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
| Index entries for sequences related to magic squares
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FORMULA
| a(n) = A000681(n)*2^[n/2]/n!.
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CROSSREFS
| Sequence in context: A007670 A074714 A064457 * A020754 A052381 A031440
Adjacent sequences: A005647 A005648 A005649 * A005651 A005652 A005653
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KEYWORD
| nonn,nice,easy
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com), Simon Plouffe (simon.plouffe(AT)gmail.com)
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EXTENSIONS
| More terms from Vladeta Jovovic (vladeta(AT)eunet.rs), Feb 11 2001
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