A270956 Number of set partitions of [n] having exactly two pairs (m,m+1) such that m+1 is in some block b and m is in block b+1.

3, 27, 159, 857, 4726, 27385, 167097, 1071422, 7203162, 50674005, 372321574, 2851766861, 22729523020, 188191920799, 1616005571254, 14370046950779, 132139869946194, 1254871372262202, 12292010800020819, 124053806137088093, 1288543305931949964

Offset

5,1

Links

Alois P. Heinz, Table of n, a(n) for n = 5..220

Wikipedia, Partition of a set

Example

a(5) = 3: 135|24, 13|25|4, 15|24|3.
a(6) = 27: 1246|35, 124|36|5, 126|35|4, 1346|25, 134|26|5, 1356|24, 135|246, 135|24|6, 136|245, 13|246|5, 13|256|4, 13|25|46, 13|25|4|6, 13|26|45, 13|2|46|5, 146|235, 14|236|5, 16|235|4, 156|24|3, 15|246|3, 15|24|36, 15|24|3|6, 16|245|3, 1|246|35, 1|24|36|5, 16|25|34, 1|26|35|4.

Crossrefs

Column k=2 of A270953.

Sequence in context: A056263 A026093 A215711 * A129530 A056370 A056361

Adjacent sequences: A270953 A270954 A270955 * A270957 A270958 A270959

Keyword

nonn

Author

Alois P. Heinz, Mar 26 2016

Status

approved