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Search: id:A000486
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| A000486 |
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One half of the number of permutations of [n] such that the differences have 4 runs with the same signs.
(Formerly M5011 N2158)
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+0
4
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| 16, 150, 926, 4788, 22548, 100530, 433162, 1825296, 7577120, 31130190, 126969558, 515183724, 2082553132, 8395437930, 33776903714, 135691891272, 544517772984, 2183315948550, 8748985781230, 35043081823140, 140313684667076
(list; graph; listen)
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OFFSET
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5,1
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REFERENCES
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N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
F. N. David, M. G. Kendall and D. E. Barton, Symmetric Function and Allied Tables, Cambridge, 1966, p. 260.
L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 260, #13
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FORMULA
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8*a(n)/4^n ->1 as n ->infinity . - DELEHAM Philippe (kolotoko(AT)wanadoo.fr), Feb 22 2004
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EXAMPLE
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a(5)=16 because the permutations of [5] with four sign runs are 13254, 14253, 14352, 15342, 15243, 21435, 21534, 23154, 24153, 25143, 31425, 31524, 32415, 32514, 41325, 42315 and their reversals.
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CROSSREFS
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a(n)=T(n, 4), where T(n, k) is the array defined in A008970.
Equals 1/2 * A060158(n).
Sequence in context: A126537 A155657 A135458 this_sequence A006420 A049351 A023014
Adjacent sequences: A000483 A000484 A000485 this_sequence A000487 A000488 A000489
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KEYWORD
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nonn
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
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Edited by Emeric Deutsch (deutsch(AT)duke.poly.edu), Feb 18 2004
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