A071088 Number of permutations that avoid the generalized pattern 12345-6.

1, 1, 2, 6, 24, 120, 719, 5022, 40064, 359400, 3580896, 39233867, 468818397, 6067548429, 84551873634, 1262188317534, 20095114167065, 339883289813330, 6086154606429378, 115025120586250896, 2288119443771888504, 47787869441095495395, 1045507132393256095282

Offset: 0

Author

Sergey Kitaev, May 26 2002

Keywords

• nonn

Links

• Alois P. Heinz, Table of n, a(n) for n = 0..450
• Sergey Kitaev, Partially Ordered Generalized Patterns, preprint.
• Sergey Kitaev, Partially Ordered Generalized Patterns, Discrete Math. 298 (2005), no. 1-3, 212-229.

Crossrefs

Cf. A071075, A071076, A071077, A177523.

Programs

Maple

b:= proc(u, o, t) option remember; `if`(u+o=0, 1, add(
      `if`(t=3 and o>j, 0, b(u+j-1, o-j, t+1)), j=1..o)+
       add(b(u-j, o+j-1, 0), j=1..u))
    end:
a:= n-> b(n, 0$2):
seq(a(n), n=0..25);  # Alois P. Heinz, Nov 14 2015

Mathematica

b[u_, o_, t_] := b[u, o, t] = If[u+o == 0, 1, Sum[If[t == 3 && o > j, 0, b[u+j-1, o-j, t+1]], {j, 1, o}] + Sum[b[u-j, o+j-1, 0], {j, 1, u}]];
a[n_] := b[n, 0, 0];
a /@ Range[0, 25] (* Jean-François Alcover, Nov 02 2020, after Alois P. Heinz *)

Formula

E.g.f.: exp(int(A(y), y=0..x)), where A(y) = 1/(Sum_{i>=0} y^{5*i}/(5*i)! - Sum_{i>=0} y^{5*i+1}/(5*i+1)!).

Let b(n) = A177523(n) = number of permutations of [n] that avoid the consecutive pattern 12345. Then a(n) = Sum_{i = 0..n-1} binomial(n-1,i)*b(i)*a(n-1-i) with a(0) = b(0) = 1. [See the recurrence for A_n and B_n in the proof of Theorem 13 in Kitaev's papers.] - Petros Hadjicostas, Nov 01 2019

Extensions

More terms from Vladeta Jovovic, May 28 2002