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A056782 Number of 3-element proper antichains (i.e., antichains such that every two members have nonempty intersection) on an unlabeled n-element set. 1
0, 0, 0, 1, 5, 18, 53, 135 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,5

LINKS

Table of n, a(n) for n=0..7.

Vladeta Jovovic, Illustration of initial terms

CROSSREFS

Cf. A001206, A047707, A051303 (labeled case), A055484, A055485, A056005.

Sequence in context: A006479 A127983 A226903 * A178684 A271771 A270990

Adjacent sequences:  A056779 A056780 A056781 * A056783 A056784 A056785

KEYWORD

more,nonn

AUTHOR

Vladeta Jovovic, Goran Kilibarda, Aug 18 2000

STATUS

approved

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Last modified May 18 15:25 EDT 2021. Contains 343995 sequences. (Running on oeis4.)