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A230344
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Number of permutations of [2n+4] in which the longest increasing run has length n+4.
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3
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1, 10, 137, 2360, 49236, 1209936, 34288800, 1102187520, 39656131200, 1579837754880, 69064610186880, 3288126441600000, 169388400557376000, 9389435419203840000, 557323393281887232000, 35272416767753797632000, 2371290445442664345600000
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OFFSET
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0,2
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COMMENTS
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Also the number of ascending runs of length n+4 in the permutations of [2n+4].
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LINKS
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FORMULA
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a(n) = (n^3+10*n^2+30*n+29)*(2*n+4)!/(n+6)! for n>0, a(0) = 1.
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MAPLE
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a:= proc(n) option remember; `if`(n<2, 1+9*n, 2*(2*n+3)*(n+2)*
(n^3+10*n^2+30*n+29)*a(n-1)/((n+6)*(n^3+7*n^2+13*n+8)))
end:
seq(a(n), n=0..25);
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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