A241632 Number of compositions of n with exactly seven descents.

21, 259, 1932, 10898, 51083, 208936, 768594, 2594957, 8158005, 24140097, 67794864, 181889780, 468678716, 1164905882, 2803070038, 6549961919, 14901997455, 33085162997, 71822232573, 152710556875, 318509850193, 652536555773, 1314728710475, 2607856668543

Offset

21,1

Links

Joerg Arndt and Alois P. Heinz, Table of n, a(n) for n = 21..1000

Example

a(21) = 21: [3,2,1,2,1,3,2,1,3,2,1], [3,2,1,3,2,1,2,1,3,2,1], [3,2,1,3,2,1,3,2,1,2,1], [2,1,3,2,1,3,2,1,3,2,1], [2,1,2,1,2,1,3,2,1,3,2,1], [3,2,1,3,2,1,2,1,2,1,2,1], [2,1,2,1,3,2,1,2,1,3,2,1], [2,1,3,2,1,2,1,3,2,1,2,1], [3,2,1,2,1,3,2,1,2,1,2,1], [3,2,1,2,1,2,1,2,1,3,2,1], [2,1,3,2,1,2,1,2,1,3,2,1], [3,2,1,2,1,2,1,3,2,1,2,1], [2,1,2,1,3,2,1,3,2,1,2,1], [2,1,3,2,1,3,2,1,2,1,2,1], [3,2,1,2,1,2,1,2,1,2,1,2,1], [2,1,2,1,2,1,2,1,2,1,3,2,1], [2,1,3,2,1,2,1,2,1,2,1,2,1], [2,1,2,1,2,1,2,1,3,2,1,2,1], [2,1,2,1,2,1,3,2,1,2,1,2,1], [2,1,2,1,3,2,1,2,1,2,1,2,1], [2,1,2,1,2,1,2,1,2,1,2,1,2,1].

Maple

b:= proc(n, i) option remember;
      `if`(n=0, 1, convert(series(add(b(n-j, j)*
      `if`(j<i, x, 1), j=1..n), x, 8), polynom))
    end:
a:= n-> coeff(b(n, 0), x, 7):
seq(a(n), n=21..50);

Mathematica

b[n_, i_] := b[n, i] = If[n == 0, 1, Sum[b[n - j, j]*
   If[j < i, x, 1], {j, 1, n}] // Expand];
a[n_] := Coefficient[b[n, 0], x, 7];
Table[a[n], {n, 21, 50}] (* Jean-François Alcover, Nov 28 2023, from Maple code *)

Crossrefs

Column k=7 of A238343 and of A238344.

Sequence in context: A365849 A360804 A322500 * A323972 A125433 A135122

Adjacent sequences: A241629 A241630 A241631 * A241633 A241634 A241635

Keyword

nonn

Author

Joerg Arndt and Alois P. Heinz, Apr 26 2014

Status

approved