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

8,2

Links

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

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 *)

Crossrefs

Column k=4 of A242352.

Sequence in context: A128801 A188484 A271037 * A178974 A233920 A017814

Adjacent sequences: A243474 A243475 A243476 * A243478 A243479 A243480

Keyword

nonn

Author

Joerg Arndt and Alois P. Heinz, Jun 05 2014

Status

approved