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A250262 Number of permutations p of [n] such that p(i) > p(i+1) iff i=1 (mod 6). 2
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 (list; graph; refs; listen; history; text; internal format)
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-Fran├žois 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

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Last modified December 14 01:19 EST 2019. Contains 329978 sequences. (Running on oeis4.)