A211309 a(n) = number |fdw(P,(n))| of entangled P-words with s=2.

1, 4, 60, 1776, 84720, 5876640, 556466400, 68882446080

Offset

1,2

Comments

See Jenca and Sarkoci for the precise definition.

Links

Table of n, a(n) for n=1..8.

Gejza Jenca and Peter Sarkoci, Linear extensions and order-preserving poset partitions, arXiv preprint arXiv:1112.5782, 2011

Formula

From Peter Bala, Sep 05 2012: (Start)

Conjectural e.g.f.: 2 - 1/A(x), where A(x) = sum {n = 0..inf} (2*n)!/2^n*x^n/n! is the e.g.f. for A000680 (also the o.g.f. for A001147).

If true, this gives a(n) = n!*A000698(n) and leads to the recurrence equation: a(n) = (2*n)!/2^n - sum {k = 1..n-1} (2*k)!/2^k*binomial(n,k)*a(n-k) with a(1) = 1.

(End)

Crossrefs

Cf. A000680, A000698, A001147.

Sequence in context: A098630 A336637 A330069 * A013502 A303286 A322450

Adjacent sequences: A211306 A211307 A211308 * A211310 A211311 A211312

Keyword

nonn

Author

N. J. A. Sloane, Apr 08 2012

Status

approved