A211311 a(n) = number |fdw(P,(n))| of entangled P-words with s=4.

1, 68, 34236, 62758896, 304863598320, 3242854167461280, 66429116436728636640, 2389384600126093124110080

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} (4*n)!/24^n*x^n/n! is the e.g.f. for A014608 (also the o.g.f. for A025036).

If true, this leads to the recurrence equation: a(n) = (4*n)!/24^n - sum {k = 1..n-1} (4*k)!/24^k*binomial(n,k)*a(n-k) with a(1) = 1.

(End)

Crossrefs

Cf. A014608, A025036.

Sequence in context: A093234 A177666 A292607 * A367529 A203757 A159385

Adjacent sequences: A211308 A211309 A211310 * A211312 A211313 A211314

Keyword

nonn

Author

N. J. A. Sloane, Apr 08 2012

Status

approved