A250263 Number of permutations p of [n] such that p(i) > p(i+1) iff i == 1 (mod 7).

1, 1, 1, 2, 3, 4, 5, 6, 7, 55, 306, 1145, 3454, 8997, 21008, 45031, 630421, 5954062, 36439007, 174011100, 697278853, 2442137774, 7677528495, 154507257827, 2060124800270, 17511127577941, 114431145225190, 619024078342189, 2890746049056048, 11979440405949527

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, 7)), j=1..u),
               add(b(u+j-1, o-j, irem(t+1, 7)), 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, 7]], {j, 1, u}], Sum[b[u + j - 1, o - j, Mod[t + 1, 7]], {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=7 of A250261.

Sequence in context: A037406 A237344 A024647 * A024648 A004858 A043312

Adjacent sequences: A250260 A250261 A250262 * A250264 A250265 A250266

Keyword

nonn

Author

Alois P. Heinz, Nov 15 2014

Status

approved