A274875 Number of set partitions of [2n] into exactly n blocks such that all odd elements are in blocks with an odd index and all even elements are in blocks with an even index.

1, 0, 1, 3, 35, 226, 3632, 36780, 770481, 10677444, 277114769, 4882093495, 151410615066, 3238949008872, 116936529884088, 2943848265346408, 121318690777898613, 3513774792447267240, 162794429514873454259, 5332375501915984656921, 274393112247007415104839

Offset: 0

Author

Alois P. Heinz, Jul 09 2016

Keywords

• nonn

Examples

			a(2) = 1: 13|24.
a(3) = 3: 13|246|5, 15|246|3, 1|246|35.
a(4) = 35: 135|246|7|8, 137|246|5|8, 13|246|57|8, 137|248|5|6, 137|24|5|68, 13|248|57|6, 13|24|57|68, 157|246|3|8, 15|246|37|8, 157|248|3|6, 157|24|3|68, 15|248|37|6, 15|24|37|68, 17|246|35|8, 1|246|357|8, 17|248|35|6, 17|24|35|68, 1|248|357|6, 1|24|357|68, 157|268|3|4, 157|26|3|48, 15|268|37|4, 15|26|37|48, 157|28|3|46, 157|2|3|468, 15|28|37|46, 15|2|37|468, 17|268|35|4, 17|26|35|48, 1|268|357|4, 1|26|357|48, 17|28|35|46, 17|2|35|468, 1|28|357|46, 1|2|357|468.
		

Links

• Alois P. Heinz, Table of n, a(n) for n = 0..300

Crossrefs

Cf. A274537.

Formula

a(n) = A274537(2n,n).