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

Author

Vladeta Jovovic, Nov 30 2000

Keywords

• more
• nonn

Comments

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

Links

• Vladeta Jovovic, Formula

Crossrefs

Row n=4 of A331508.

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

Extensions

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

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