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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
1, 4, 25, 278, 5532, 200589, 11662671, 981458725, 111213730857, 16212510876591, 2947663429595884, 653299790376494253 (list; graph; refs; listen; history; text; internal format)
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..12.

Vladeta Jovovic, Formula

CROSSREFS

Row n=4 of A331508.

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

Sequence in context: A308008 A144281 A320569 * A216660 A238510 A222982

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

STATUS

approved

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Last modified February 28 05:24 EST 2021. Contains 341695 sequences. (Running on oeis4.)