A271789 Number of set partitions of [n] having exactly two pairs (m,m+1) such that m is in some block b and m+1 is in block b+1.

0, 1, 6, 24, 86, 307, 1143, 4513, 18956, 84546, 399218, 1989792, 10439521, 57504306, 331747730, 1999924893, 12571830681, 82245682149, 558951842996, 3939679356783, 28754596249395, 217019729585609, 1691485555633721, 13598390501982510, 112633410446366669

Offset

2,3

Links

Alois P. Heinz, Table of n, a(n) for n = 2..400

Example

a(3) = 1: 1|2|3.
a(4) = 6: 12|3|4, 13|24, 1|23|4, 14|2|3, 1|24|3, 1|2|34.
a(5) = 24: 123|4|5, 124|35, 12|34|5, 125|3|4, 12|35|4, 12|3|45, 134|25, 135|24, 13|245, 13|2|4|5, 14|235, 1|234|5, 15|23|4, 1|235|4, 1|23|45, 145|2|3, 14|2|35, 14|2|3|5, 15|24|3, 1|245|3, 1|24|3|5, 15|2|34, 1|25|34, 1|2|345.

Crossrefs

Column k=2 of A185982.

Sequence in context: A317408 A166060 A124807 * A121532 A025472 A255474

Adjacent sequences: A271786 A271787 A271788 * A271790 A271791 A271792

Keyword

nonn

Author

Alois P. Heinz, Apr 14 2016

Status

approved