A058791 Number of covers of an unlabeled n-set such that every point of the set is covered by exactly 4 subsets of the cover and that intersection of every 4 subsets of the cover contains at most one point.

1, 4, 25, 278, 5532, 200589, 11662671, 981458725, 111213730857, 16212510876591, 2947663429595884, 653299790376494253, 173373367472722467460, 54295204354760461199529, 19822683467350158062736540

Offset

1,2

Comments

Cover may include multiple occurrences of a subset. Also n-rowed binary matrices with distinct rows and all row sums 4.

Links

Table of n, a(n) for n=1..15.

Vladeta Jovovic, Formula

Crossrefs

Row n=4 of A331508.

Cf. A050535, A050913, A058783, A058784, A058785.

Sequence in context: A144281 A361589 A320569 * A216660 A352859 A350585

Adjacent sequences: A058788 A058789 A058790 * A058792 A058793 A058794

Keyword

more,nonn

Author

Vladeta Jovovic, Nov 30 2000

Extensions

a(8)-a(12) from Andrew Howroyd, Jan 29 2020

a(13)-a(15) from Sean A. Irvine, Aug 26 2022

Status

approved