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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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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: A125379 A126537 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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njas
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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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