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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. 6

%I

%S 1,3,12,66,445,4279,53340,846254,16333946,371976963,9763321109,

%T 290473143807,9674133467729,357177322891321,14503958827502886,

%U 643502334799711633,31018731336031551119,1616523352051185316626,90689288905913623412837,5456178840303106057314759,350830170593891706361540379

%N 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.

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

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

%H Vladeta Jovovic, <a href="/A058790/a058790.pdf">Formula</a>

%Y Cf. A050535, A050913, A058783-A058785, A082789, A082790.

%K nonn

%O 1,2

%A _Vladeta Jovovic_, Nov 30 2000

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

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Last modified January 18 01:05 EST 2020. Contains 330995 sequences. (Running on oeis4.)