A058790 Number of covers of an unlabeled n-set such that every point of the set is covered by exactly 3 subsets of the cover and that intersection of every 3 subsets of the cover contains at most one point.

1, 3, 12, 66, 445, 4279, 53340, 846254, 16333946, 371976963, 9763321109, 290473143807, 9674133467729, 357177322891321, 14503958827502886, 643502334799711633, 31018731336031551119, 1616523352051185316626, 90689288905913623412837, 5456178840303106057314759, 350830170593891706361540379

Offset: 1

Author

Vladeta Jovovic, Nov 30 2000

Keywords

• nonn

Comments

Cover may include multiple occurrences of a subset. Also n-rowed binary matrices with distinct rows and all row sums 3.

References

• For labeled case see Goulden I. P., Jackson D. M., Combinatorial Enumeration, John Wiley and Sons, New York, 1983.

Links

• Vladeta Jovovic, Formula

Crossrefs

Row n=3 of A331508.

Cf. A050535, A050913, A058783, A058784, A058785, A082789, A082790.

Extensions

More terms from T. Forbes (anthony.d.forbes(AT)googlemail.com), May 24 2003