OFFSET
0,1
COMMENTS
A set system (set of sets) is an antichain if no edge is a subset of any other, and is intersecting if no two edges are disjoint.
FORMULA
a(n) = A001206(n + 1) + 1.
EXAMPLE
The a(0) = 2 through a(3) = 13 antichains:
{} {} {} {}
{{}} {{}} {{}} {{}}
{{1}} {{1}} {{1}}
{{2}} {{2}}
{{1,2}} {{3}}
{{1,2}}
{{1,3}}
{{2,3}}
{{1,2,3}}
{{1,2},{1,3}}
{{1,2},{2,3}}
{{1,3},{2,3}}
{{1,2},{1,3},{2,3}}
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Gus Wiseman, Jul 01 2019
STATUS
approved