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 A280889 Number of set partitions of [2n] into exactly n blocks where sizes of distinct blocks are coprime. 1
 1, 1, 4, 75, 56, 6930, 28512, 2849847, 972400, 693870606, 99936200, 63488350926, 475814969280, 166184959669300, 497980728000, 78877488833249175, 1489333512849120, 1116126129558913110, 1597083864660900000, 4467282986266589095530, 107279471180408841600 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS Wikipedia, Coprime integers Wikipedia, Partition of a set FORMULA a(n) = A280880(2n,n). EXAMPLE a(1) = 1: 12. a(2) = 4: 123|4, 124|3, 134|2, 1|234. a(4) = 56 = binomial(8,3): 12345|6|7|8, 12346|5|7|8, 12347|5|6|8, ..., 1|25678|3|4, 1|2|35678|4, 1|2|3|45678. CROSSREFS Cf. A280880. Sequence in context: A000857 A240007 A046057 * A257367 A072373 A006412 Adjacent sequences:  A280886 A280887 A280888 * A280890 A280891 A280892 KEYWORD nonn AUTHOR Alois P. Heinz, Jan 09 2017 STATUS approved

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Last modified May 17 22:15 EDT 2021. Contains 343992 sequences. (Running on oeis4.)