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A243475 Number of isoscent sequences of length n with exactly two descents. 2
2, 28, 241, 1667, 10142, 56748, 299485, 1514445, 7415873, 35424718, 165963977, 765639729, 3488740303, 15739196772, 70434524941, 313136541466, 1384706596078, 6096641331963, 26747810596747, 117015840972949, 510745056446585, 2225207050547044, 9680854941464722 (list; graph; refs; listen; history; text; internal format)
OFFSET

5,1

LINKS

Joerg Arndt and Alois P. Heinz, Table of n, a(n) for n = 5..100

EXAMPLE

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

MATHEMATICA

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 *)

CROSSREFS

Column k=2 of A242352.

Sequence in context: A281124 A244721 A001759 * A019441 A147537 A183067

Adjacent sequences:  A243472 A243473 A243474 * A243476 A243477 A243478

KEYWORD

nonn

AUTHOR

Joerg Arndt and Alois P. Heinz, Jun 05 2014

STATUS

approved

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Last modified July 18 11:48 EDT 2019. Contains 325139 sequences. (Running on oeis4.)