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A283877 Number of non-isomorphic set-systems of weight n. 95
1, 2, 4, 9, 18, 44, 98, 244, 605 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

A set-system is a finite set of finite nonempty sets. The weight of a set-system is the sum of cardinalities of its elements.

LINKS

Table of n, a(n) for n=1..9.

EXAMPLE

Non-isomorphic representatives of the a(4)=9 set-systems are:

((1234)),

((1)(234)), ((3)(123)), ((12)(34)), ((13)(23)),

((1)(2)(12)), ((1)(2)(34)), ((1)(3)(23)),

((1)(2)(3)(4)).

CROSSREFS

Cf. A007716, A034691, A049311, A056156, A089259, A116540.

Sequence in context: A259803 A032175 A000678 * A319567 A081490 A292478

Adjacent sequences:  A283874 A283875 A283876 * A283878 A283879 A283880

KEYWORD

nonn,more

AUTHOR

Gus Wiseman, Mar 17 2017

STATUS

approved

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Last modified October 22 23:18 EDT 2018. Contains 316518 sequences. (Running on oeis4.)