OFFSET
0,2
FORMULA
E.g.f.: (log(A(exp(x)-1))+1)*A(exp(x)-1) where A(x) is the e.g.f. for A001035.
EXAMPLE
a(2) = 9. Let X = {a,b}. There are four distinct topologies (A000798) that can be placed on X: {{},X} {{},{a},X} {{}, {b},X} {{},{a},{b},X}. These topologies have 2 + 2 + 2 + 3 sets respectively that are open and closed and connected.
CROSSREFS
KEYWORD
nonn
AUTHOR
Geoffrey Critzer, Apr 02 2017
STATUS
approved