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

2, 28, 241, 1667, 10142, 56748, 299485, 1514445, 7415873, 35424718, 165963977, 765639729, 3488740303, 15739196772, 70434524941, 313136541466, 1384706596078, 6096641331963, 26747810596747, 117015840972949, 510745056446585, 2225207050547044, 9680854941464722

Offset: 5

Author

Joerg Arndt and Alois P. Heinz, Jun 05 2014

Keywords

• nonn

Examples

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

Links

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

Crossrefs

Column k=2 of A242352.

Programs

Mathematica

b[n_, i_, t_] := b[n, i, t] = If[n<1, 1, Expand[Sum[If[jJean-François Alcover, Feb 09 2015, after A242352 *)