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A230382
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Number of ascending runs of length n in the permutations of [2n].
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2
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1, 2, 21, 312, 5880, 133920, 3575880, 109549440, 3788104320, 145957593600, 6201593798400, 288084016281600, 14525808782284800, 790129980896256000, 46120599397192320000, 2875600728738017280000, 190740227037467627520000, 13411608375592258191360000
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OFFSET
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0,2
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LINKS
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FORMULA
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MAPLE
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a:= proc(n) option remember; `if`(n<2, 1+n,
2*(2*n-1)*(n+1)*(n^2+n+1)*a(n-1)/((n+2)*(n^2-n+1)))
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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