

A305935


Number of labeled spanning intersecting setsystems on n vertices with no singletons.


3



1, 0, 1, 12, 809, 1146800, 899927167353, 291136684655893185321964, 14704020783497694096988185391720223222562121969, 12553242487939982849962414795232892198542733492886483991398790450208264017757788101836749760
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OFFSET

0,4


COMMENTS

An intersecting setsystem S is a finite set of finite nonempty sets (edges), any two of which have a nonempty intersection. S is spanning if every vertex is contained in some edge. A singleton is an edge containing only one vertex.


LINKS



FORMULA



EXAMPLE

The a(3) = 12 spanning intersecting setsystems with no singletons:
{{1,2,3}}
{{1,2},{1,3}}
{{1,2},{2,3}}
{{1,3},{2,3}}
{{1,2},{1,2,3}}
{{1,3},{1,2,3}}
{{2,3},{1,2,3}}
{{1,2},{1,3},{2,3}}
{{1,2},{1,3},{1,2,3}}
{{1,2},{2,3},{1,2,3}}
{{1,3},{2,3},{1,2,3}}
{{1,2},{1,3},{2,3},{1,2,3}}


CROSSREFS

Cf. A001206, A006126, A051185, A048143, A058891, A305001, A305843, A305844, A305854A305857, A305999, A306000, A306001, A306008.


KEYWORD

nonn


AUTHOR



EXTENSIONS



STATUS

approved



