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A317282
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Number of permutations of [n] with exactly two increasing runs of even length.
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2
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5, 43, 258, 1853, 15634, 133697, 1207256, 11974457, 126980013, 1421291622, 16925790480, 213992804118, 2851968574855, 39996895523591, 589713707701692, 9114791365659163, 147335664946835342, 2486973983349027871, 43763134470537718258, 801419373432471123541
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OFFSET
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4,1
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LINKS
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Alois P. Heinz, Table of n, a(n) for n = 4..472
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MAPLE
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b:= proc(u, o, t) option remember; series(`if`(u+o=0, x^t,
add(b(u+j-1, o-j, irem(t+1, 2)), j=1..o)+
add(b(u-j, o+j-1, 0)*x^t, j=1..u)), x, 3)
end:
a:= n-> coeff(b(n, 0$2), x, 2):
seq(a(n), n=4..30);
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CROSSREFS
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Column k=2 of A097592.
Sequence in context: A173554 A126963 A221874 * A182191 A038140 A178826
Adjacent sequences: A317279 A317280 A317281 * A317283 A317284 A317285
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KEYWORD
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nonn
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AUTHOR
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Alois P. Heinz, Jul 25 2018
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STATUS
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approved
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