OFFSET
0,4
LINKS
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
G.f.: S(x, y) is the unique power series solution of the equation S(x, y) = 1 + S(x, y)^2 * x / (1 + x) + S(x, y)^3 * y.
EXAMPLE
There are 28 skeleta of (3+1)-free posets with 1 clone set and 2 tangles.
Table begins
1 1 3 12 55 273 ...
1 5 28 165 1001 6188 ...
1 16 152 1265 9919 75208 ...
2 47 658 7315 71981 657356 ...
4 136 2547 35975 431599 4660516 ...
9 392 9252 159701 2277821 28589750 ...
......................................
CROSSREFS
KEYWORD
AUTHOR
Mathieu Guay-Paquet, Jan 18 2013
STATUS
approved