A270957 Number of set partitions of [n] having exactly three pairs (m,m+1) such that m+1 is in some block b and m is in block b+1.

1, 21, 197, 1421, 9573, 64724, 449567, 3230230, 24053169, 185658621, 1484943532, 12299106220, 105400873263, 933717036862, 8541991253431, 80620086997245, 784225175253212, 7854824886117957, 80933906884404094, 857116366195307414, 9321782438290435408

Offset: 6

Author

Alois P. Heinz, Mar 26 2016

Keywords

• nonn

Examples

			a(6) = 1: 136|25|4.
a(7) = 21: 1247|36|5, 1347|26|5, 1357|246, 135|247|6, 137|246|5, 1367|25|4, 136|257|4, 136|25|47, 136|25|4|7, 137|256|4, 13|257|46, 13|25|47|6, 137|26|45, 13|27|46|5, 147|236|5, 157|246|3, 15|247|36, 15|24|37|6, 17|246|35, 1|247|36|5, 17|26|35|4.
		

Links

• Alois P. Heinz, Table of n, a(n) for n = 6..220
• Wikipedia, Partition of a set

Crossrefs

Column k=3 of A270953.