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%I #10 Feb 10 2015 05:59:59
%S 1,2,6,20,80,366,1897,10976,70155,490930,3733246,30655152,270334766,
%T 2548153230,25566585450,272052199520,3060191748695,36282298766760,
%U 452220051658265,5911274512571280,80862988937379390,1155309461910323610,17208404375488550100
%N Number of ascent sequences of length n with exactly one flat step.
%H Joerg Arndt and Alois P. Heinz, <a href="/A242154/b242154.txt">Table of n, a(n) for n = 2..140</a>
%F a(n) ~ 2*sqrt(3)/(exp(Pi^2/12)*sqrt(Pi)) * (6/Pi^2)^n * n! * sqrt(n). - _Vaclav Kotesovec_, Aug 27 2014
%t 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, 1]; Table[ a[n], {n, 2, 30}] (* _Jean-François Alcover_, Feb 10 2015, after A242153 *)
%Y Column k=1 of A242153.
%K nonn
%O 2,2
%A _Joerg Arndt_ and _Alois P. Heinz_, May 05 2014
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