A250266 Number of permutations p of [n] such that p(i) > p(i+1) iff i == 1 (mod 10).

1, 1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 109, 768, 3627, 13636, 43665, 123744, 318223, 755802, 1679581, 3527140, 70542781, 878845662, 7113969943, 44573747024, 231938007625, 1043938332476, 4176060103827, 15138650342428, 50462774778029, 156435448534980

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, 10)), j=1..u),
               add(b(u+j-1, o-j, irem(t+1, 10)), 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, 10]], {j, 1, u}], Sum[b[u + j - 1, o - j, Mod[t + 1, 10]], {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=10 of A250261.

Sequence in context: A111705 A071274 A258373 * A357936 A085908 A110304

Adjacent sequences: A250263 A250264 A250265 * A250267 A250268 A250269

Keyword

nonn

Author

Alois P. Heinz, Nov 15 2014

Status

approved