A079145 Number of labeled semitransitive orders on n elements: (1+3)-free posets.

1, 3, 19, 195, 2791, 51423, 1167979, 32067675, 1064281951, 43806954183, 2376985075939, 186194963282595, 22598045194449271, 4259417828951807343, 1200382884654622348699, 490727012583769876310955, 286998078380075662131967951, 238889878466868543045084230103

Offset

1,2

Links

Table of n, a(n) for n=1..18.

M. Guay-Paquet, A. H. Morales, E. Rowland, Structure and enumeration of (3+1)-free posets (extended abstract), arXiv:1212.5356 [math.CO], 2012.

Formula

E.g.f.: S(e^x-1, T(x)), where S(x, y) is the g.f. for A221494 and T(x) is the e.g.f. for A221493. [Mathieu Guay-Paquet, Jan 18 2013]

Crossrefs

Cf. A079146 (unlabeled semitransitive orders).

Sequence in context: A108292 A053554 A048172 * A000763 A001832 A195511

Adjacent sequences: A079142 A079143 A079144 * A079146 A079147 A079148

Keyword

nonn,easy

Author

Detlef Pauly (dettodet(AT)yahoo.de), Dec 27 2002

Extensions

More terms from Mathieu Guay-Paquet, Jan 18 2013

Status

approved