A250262 Number of permutations p of [n] such that p(i) > p(i+1) iff i == 1 (mod 6).

1, 1, 1, 2, 3, 4, 5, 6, 41, 208, 711, 1970, 4741, 10284, 123397, 1041224, 5690415, 24359248, 87922385, 278723178, 4777712981, 56439873880, 424119250083, 2456329637366, 11821181689417, 49308397822776, 1098781192727401, 16688667550625072, 159609583197355203

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, 6)), j=1..u),
               add(b(u+j-1, o-j, irem(t+1, 6)), 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, 6]], {j, 1, u}], Sum[b[u + j - 1, o - j, Mod[t + 1, 6]], {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=6 of A250261.

Sequence in context: A300856 A173575 A024641 * A043311 A171594 A044908

Adjacent sequences: A250259 A250260 A250261 * A250263 A250264 A250265

Keyword

nonn

Author

Alois P. Heinz, Nov 15 2014

Status

approved