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A242162
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Number of ascent sequences of length n with exactly nine flat steps.
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3
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1, 10, 110, 1100, 11440, 122122, 1356355, 15695680, 189496450, 2386901660, 31351799908, 429069944160, 6112269059260, 90535884261900, 1392850530925700, 22231833692574880, 367758543399421625, 6298103145093331000, 111551381242802518875, 2041429096543928691600
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OFFSET
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10,2
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LINKS
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FORMULA
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a(n) ~ Pi^(31/2) / (9! * 6^7 * sqrt(3)*exp(Pi^2/12)) * (6/Pi^2)^n * n! * sqrt(n). - Vaclav Kotesovec, Aug 27 2014
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MATHEMATICA
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b[n_, i_, t_] := b[n, i, t] = If[n == 0, 1, Expand[Sum[ If[j == i, x, 1]*b[n - 1, j, t + If[j > i, 1, 0]], {j, 0, t + 1}]]]; a[n_] := Coefficient[b[n, -1, -1], x, 9]; Table[a[n], {n, 10, 30}] (* Jean-François Alcover, Feb 10 2015, after A242153 *)
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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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