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A306000 Number of labeled intersecting set-systems with no singletons covering some subset of {1,...,n}. 3
1, 1, 2, 16, 864, 1150976, 899934060544, 291136684662192699604992, 14704020783497694096990514485197495566069661696, 12553242487939982849962414795232892198542733625222671042878037323112413463887484853594095616 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

An intersecting set-system S is a finite set of finite nonempty sets (edges), any two of which have a nonempty intersection. A singleton is an edge containing only one vertex.

LINKS

Table of n, a(n) for n=0..9.

FORMULA

a(n) = A051185(n) - n*2^(2^(n-1)-1). - Andrew Howroyd, Aug 12 2019

EXAMPLE

The a(3) = 16 set-systems:

  {}

  {{1,2}}

  {{1,3}}

  {{2,3}}

  {{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, A305854-A305857, A305935, A305999, A306001.

Sequence in context: A013005 A013000 A013178 * A084595 A273193 A002543

Adjacent sequences:  A305997 A305998 A305999 * A306001 A306002 A306003

KEYWORD

nonn

AUTHOR

Gus Wiseman, Jun 16 2018

EXTENSIONS

a(6)-a(9) from Andrew Howroyd, Aug 12 2019

STATUS

approved

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Last modified October 27 20:18 EDT 2021. Contains 348290 sequences. (Running on oeis4.)