OFFSET
0,2
FORMULA
E.g.f.: the diagonal of exp( Sum_B x^|lB| * y^|rB| / |Aut(B,lB,rB)| ), where B runs over connected squarefree bipartite graphs with ordered bipartitions, (lB,rB) is the bipartition of B, and Aut(B,lB,rB) is the group of automorphisms of B preserving its bipartition.
CROSSREFS
KEYWORD
hard,more,nonn
AUTHOR
Max Alekseyev, Jul 03 2010
EXTENSIONS
a(6)-a(8) from Hiroaki Yamanouchi, Aug 27 2014
a(9)-a(11) from Max Alekseyev, Feb 26 2022
STATUS
approved