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A304981 Number of unlabeled clutters (connected antichains) spanning up to n vertices without singleton edges. 7
1, 1, 2, 5, 19, 176, 16118, 489996568 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

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

FORMULA

Partial sums of A261006(n > 0).

EXAMPLE

Non-isomorphic representatives of the a(3) = 5 clutters:

  {}

  {{1,2}}

  {{1,2,3}}

  {{1,3},{2,3}}

  {{1,2},{1,3},{2,3}}

Non-isomorphic representatives of the a(4) = 19 clutters:

  {}

  {{1,2}}

  {{1,2,3}}

  {{1,2,3,4}}

  {{1,3},{2,3}}

  {{1,4},{2,3,4}}

  {{1,3,4},{2,3,4}}

  {{1,2},{1,3},{2,3}}

  {{1,2},{1,3,4},{2,3,4}}

  {{1,3},{1,4},{2,3,4}}

  {{1,3},{2,4},{3,4}}

  {{1,4},{2,4},{3,4}}

  {{1,2,4},{1,3,4},{2,3,4}}

  {{1,2},{1,3},{1,4},{2,3,4}}

  {{1,2},{1,3},{2,4},{3,4}}

  {{1,4},{2,3},{2,4},{3,4}}

  {{1,2,3},{1,2,4},{1,3,4},{2,3,4}}

  {{1,3},{1,4},{2,3},{2,4},{3,4}}

  {{1,2},{1,3},{1,4},{2,3},{2,4},{3,4}}

CROSSREFS

Cf. A048143, A198085, A261006, A304912, A304981, A304982, A304983, A304984, A304985, A304986.

Sequence in context: A039719 A198203 A014466 * A284860 A108799 A193674

Adjacent sequences:  A304978 A304979 A304980 * A304982 A304983 A304984

KEYWORD

nonn

AUTHOR

Gus Wiseman, May 23 2018

STATUS

approved

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Last modified February 21 04:18 EST 2019. Contains 320371 sequences. (Running on oeis4.)