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

1, 1, 4, 75, 56, 6930, 28512, 2849847, 972400, 693870606, 99936200, 63488350926, 475814969280, 166184959669300, 497980728000, 78877488833249175, 1489333512849120, 1116126129558913110, 1597083864660900000, 4467282986266589095530, 107279471180408841600

Offset

0,3

Links

Table of n, a(n) for n=0..20.

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