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A280889 Number of set partitions of [2n] into exactly n blocks where sizes of distinct blocks are coprime. 1

%I #6 Jan 12 2017 14:39:53

%S 1,1,4,75,56,6930,28512,2849847,972400,693870606,99936200,63488350926,

%T 475814969280,166184959669300,497980728000,78877488833249175,

%U 1489333512849120,1116126129558913110,1597083864660900000,4467282986266589095530,107279471180408841600

%N Number of set partitions of [2n] into exactly n blocks where sizes of distinct blocks are coprime.

%H Wikipedia, <a href="https://en.wikipedia.org/wiki/Coprime_integers">Coprime integers</a>

%H Wikipedia, <a href="https://en.wikipedia.org/wiki/Partition_of_a_set">Partition of a set</a>

%F a(n) = A280880(2n,n).

%e a(1) = 1: 12.

%e a(2) = 4: 123|4, 124|3, 134|2, 1|234.

%e 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.

%Y Cf. A280880.

%K nonn

%O 0,3

%A _Alois P. Heinz_, Jan 09 2017

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Last modified March 29 11:14 EDT 2024. Contains 371278 sequences. (Running on oeis4.)