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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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3
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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; refs; listen; history; internal format)
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OFFSET
| 5,1
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REFERENCES
| L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 260, #13
F. N. David, M. G. Kendall and D. E. Barton, Symmetric Function and Allied Tables, Cambridge, 1966, p. 260.
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).
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FORMULA
| 8*a(n)/4^n ->1 as n ->infinity . - DELEHAM Philippe (kolotoko(AT)wanadoo.fr), Feb 22 2004
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EXAMPLE
| 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
| a(n)=T(n, 4), where T(n, k) is the array defined in A008970.
Equals 1/2 * A060158(n).
Sequence in context: A178259 A155657 A135458 * A006420 A049351 A023014
Adjacent sequences: A000483 A000484 A000485 * A000487 A000488 A000489
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KEYWORD
| nonn
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
| Edited by Emeric Deutsch (deutsch(AT)duke.poly.edu), Feb 18 2004
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