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 A211309 a(n) = number |fdw(P,(n))| of entangled P-words with s=2. 0
 1, 4, 60, 1776, 84720, 5876640, 556466400, 68882446080 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 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 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: A013485 A324959 A098630 * A013502 A303286 A322450 Adjacent sequences:  A211306 A211307 A211308 * A211310 A211311 A211312 KEYWORD nonn AUTHOR N. J. A. Sloane, Apr 08 2012 STATUS approved

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Last modified March 21 04:59 EDT 2019. Contains 321364 sequences. (Running on oeis4.)