A243477 Number of isoscent sequences of length n with exactly four descents.

1, 98, 2637, 44051, 563444, 6054955, 57523592, 498540949, 4024955854, 30719216646, 224034574434, 1573966189886, 10719427410360, 71119561115093, 461496506508538, 2938387657219301, 18406158143420637, 113681266064450777, 693570688210367081, 4186481577282095644

Offset: 8

Author

Joerg Arndt and Alois P. Heinz, Jun 05 2014

Keywords

• nonn

Links

• Joerg Arndt and Alois P. Heinz, Table of n, a(n) for n = 8..100

Crossrefs

Column k=4 of A242352.

Programs

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, 4]; Table[a[n], {n, 8, 40}] (* Jean-François Alcover, Feb 09 2015, after A242352 *)