This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A280889 #6 Jan 12 2017 14:39:53 %S A280889 1,1,4,75,56,6930,28512,2849847,972400,693870606,99936200,63488350926, %T A280889 475814969280,166184959669300,497980728000,78877488833249175, %U A280889 1489333512849120,1116126129558913110,1597083864660900000,4467282986266589095530,107279471180408841600 %N A280889 Number of set partitions of [2n] into exactly n blocks where sizes of distinct blocks are coprime. %H A280889 Wikipedia, <a href="https://en.wikipedia.org/wiki/Coprime_integers">Coprime integers</a> %H A280889 Wikipedia, <a href="https://en.wikipedia.org/wiki/Partition_of_a_set">Partition of a set</a> %F A280889 a(n) = A280880(2n,n). %e A280889 a(1) = 1: 12. %e A280889 a(2) = 4: 123|4, 124|3, 134|2, 1|234. %e A280889 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 A280889 Cf. A280880. %K A280889 nonn %O A280889 0,3 %A A280889 _Alois P. Heinz_, Jan 09 2017