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Search: id:A018241
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| A018241 |
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Number of simple allowable sequences on 1..n. |
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+0
3
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| 1, 1, 2, 32, 4608, 7028736, 132089118720, 34998332896051200, 147462169661142781132800, 11008782516353752266715850342400, 16061608070479103314001351327405309952000
(list; graph; listen)
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OFFSET
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1,3
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REFERENCES
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J. E. Goodman and J. O'Rourke, editors, Handbook of Discrete and Computational Geometry, CRC Press, 1997, p. 102.
G. Kreweras, Sur un probleme de scrutin a plus de deux candidats, Publications de l'Institut de Statistique de l'Universit\'{e} de Paris, 26 (1981), 69-87.
R. P. Stanley, On the number of reduced decompositions of elements of certain groups, European J. Combin., 5 (1984), 359-372.
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FORMULA
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(n-2)!*C(n, 2)!/(1^{n-1} . 3^{n-2} ... (2n-3)^1 ).
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MAPLE
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A018241 := proc(n) local i; (n-2)!*binomial(n, 2)!/product( (2*i+1)^(n-i-1), i=0..n-2 ); end;
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CROSSREFS
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Cf. A003121, A005118.
Sequence in context: A068183 A166077 A053853 this_sequence A012599 A129349 A091804
Adjacent sequences: A018238 A018239 A018240 this_sequence A018242 A018243 A018244
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KEYWORD
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nonn,easy,nice
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com).
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