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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
 1, 3, 12, 66, 445, 4279, 53340, 846254, 16333946, 371976963, 9763321109, 290473143807, 9674133467729, 357177322891321, 14503958827502886, 643502334799711633, 31018731336031551119, 1616523352051185316626, 90689288905913623412837, 5456178840303106057314759, 350830170593891706361540379 (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 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 Cf. A050535, A050913, A058783-A058785, A082789, A082790. Sequence in context: A007871 A214565 A267323 * A199746 A293302 A248871 Adjacent sequences:  A058787 A058788 A058789 * A058791 A058792 A058793 KEYWORD nonn AUTHOR Vladeta Jovovic, Nov 30 2000 EXTENSIONS More terms from T. Forbes (anthony.d.forbes(AT)googlemail.com), May 24, 2003 STATUS approved

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Last modified December 6 04:14 EST 2019. Contains 329784 sequences. (Running on oeis4.)