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

Author

Alois P. Heinz, Nov 15 2014

Keywords

• nonn

Links

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

Crossrefs

Column k=10 of A250261.

Programs

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 *)