A211310 a(n) = number |fdw(P,(n))| of entangled P-words with s=3.

1, 18, 1566, 354456, 163932120, 134973740880, 180430456454640, 366311352681348480

Offset: 1

Author

N. J. A. Sloane, Apr 08 2012

Keywords

• nonn

Comments

See Jenca and Sarkoci for the precise definition.

Links

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

Crossrefs

Cf. A014606, A025035.

Formula

From Peter Bala, Sep 05 2012: (Start)

Conjectural e.g.f.: 2 - 1/A(x), where A(x) = sum {n = 0..inf} (3*n)!/6^n*x^n/n! is the e.g.f. for A014606 (also the o.g.f. for A025035).

If true, this leads to the recurrence equation: a(n) = (3*n)!/6^n - sum {k = 1..n-1} (3*k)!/6^k*binomial(n,k)*a(n-k) with a(1) = 1.

(End)