OFFSET
0,4
COMMENTS
Also number of connected antichains on a labeled n-set.
LINKS
Patrick De Causmaecker, Stefan De Wannemacker, On the number of antichains of sets in a finite universe, arXiv:1407.4288 [math.CO], 2014.
Greg Huber, Letters to N. J. A. Sloane, May 1983 [Annotated, corrected, scanned copy]
Gus Wiseman, Every Clutter Is a Tree of Blobs, The Mathematica Journal, Vol. 19, 2017.
EXAMPLE
For n=3 we could have 2 edges (in 3 ways), 3 edges (1 way), or 3 edges and a triangle (1 way), so a(3)=5.
a(5) = 1+75+645+1655+2005+1345+485+115+20+2 = 6348.
CROSSREFS
KEYWORD
nonn,nice,more
AUTHOR
Greg Huber, May 12 1983
EXTENSIONS
More terms from Vladeta Jovovic, Jun 17 2006
Entry revised by N. J. A. Sloane, Jul 27 2006
STATUS
approved