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A243475 Number of isoscent sequences of length n with exactly two descents. 2

%I

%S 2,28,241,1667,10142,56748,299485,1514445,7415873,35424718,165963977,

%T 765639729,3488740303,15739196772,70434524941,313136541466,

%U 1384706596078,6096641331963,26747810596747,117015840972949,510745056446585,2225207050547044,9680854941464722

%N Number of isoscent sequences of length n with exactly two descents.

%H Joerg Arndt and Alois P. Heinz, <a href="/A243475/b243475.txt">Table of n, a(n) for n = 5..100</a>

%e a(5) = 2: [0,0,2,1,0], [0,1,0,1,0].

%t b[n_, i_, t_] := b[n, i, t] = If[n<1, 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, 0, 0], x, 2]; Table[a[n], {n, 5, 40}] (* _Jean-Fran├žois Alcover_, Feb 09 2015, after A242352 *)

%Y Column k=2 of A242352.

%K nonn

%O 5,1

%A _Joerg Arndt_ and _Alois P. Heinz_, Jun 05 2014

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Last modified October 18 10:25 EDT 2019. Contains 328146 sequences. (Running on oeis4.)