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Search: id:A097593
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| A097593 |
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Number of increasing runs of even length in all permutations of [n]. |
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+0
1
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| 0, 0, 1, 4, 22, 138, 998, 8174, 74898, 759634, 8451862, 102381222, 1341503546, 18907621562, 285259758366, 4587192222958, 78327809126818, 1415429225667234, 26987142531214118, 541434621007942454, 11402270678456333322
(list; graph; listen)
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OFFSET
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0,4
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FORMULA
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E.g.f.=[4(exp(-x)-1)+4x-x^2]/[2(1-x)^2].
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EXAMPLE
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Example: a(3)=4 because we have 123,(13)2,2(13),(23)1,3(12),321 (runs of even length shown between parentheses).
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MAPLE
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G:=(4*(exp(-x)-1)+4*x-x^2)/2/(1-x)^2: Gser:=series(G, x=0, 25): 0, seq(n!*coeff(Gser, x^n), n=1..24);
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CROSSREFS
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Sequence in context: A007196 A091638 A142984 this_sequence A025756 A002293 A003287
Adjacent sequences: A097590 A097591 A097592 this_sequence A097594 A097595 A097596
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KEYWORD
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nonn
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AUTHOR
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Emeric Deutsch (deutsch(AT)duke.poly.edu), Aug 29 2004
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