A250265 Number of permutations p of [n] such that p(i) > p(i+1) iff i == 1 (mod 9).

1, 1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 89, 583, 2562, 8996, 27013, 72057, 175016, 393805, 831384, 14964895, 171416216, 1274511567, 7351608748, 35319494255, 147208687584, 546836589610, 1845658907261, 5742168041637, 149870423643695, 2452427105334001, 25693720399771170

Offset

0,4

Links

Alois P. Heinz, Table of n, a(n) for n = 0..500

Maple

b:= proc(u, o, t) option remember; `if`(u+o=0, 1,
     `if`(t=1, add(b(u-j, o+j-1, irem(t+1, 9)), j=1..u),
               add(b(u+j-1, o-j, irem(t+1, 9)), j=1..o)))
    end:
a:= n-> b(0, n, 0):
seq(a(n), n=0..35);

Mathematica

b[u_, o_, t_] := b[u, o, t] = If[u + o == 0, 1, If[t == 1, Sum[b[u - j, o + j - 1, Mod[t + 1, 9]], {j, 1, u}], Sum[b[u + j - 1, o - j, Mod[t + 1, 9]], {j, 1, o}]]];
a[n_] := b[0, n, 0];
Table[a[n], {n, 0, 35}] (* Jean-François Alcover, Jul 22 2019, after Alois P. Heinz *)

Crossrefs

Column k=9 of A250261.

Sequence in context: A032799 A208130 A160343 * A239085 A273478 A278944

Adjacent sequences: A250262 A250263 A250264 * A250266 A250267 A250268

Keyword

nonn

Author

Alois P. Heinz, Nov 15 2014

Status

approved