A270956 - OEIS

%I #5 Mar 27 2016 14:26:03

%S 3,27,159,857,4726,27385,167097,1071422,7203162,50674005,372321574,

%T 2851766861,22729523020,188191920799,1616005571254,14370046950779,

%U 132139869946194,1254871372262202,12292010800020819,124053806137088093,1288543305931949964

%N 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.

%H Alois P. Heinz, <a href="/A270956/b270956.txt">Table of n, a(n) for n = 5..220</a>

%H Wikipedia, <a href="https://en.wikipedia.org/wiki/Partition_of_a_set">Partition of a set</a>

%e a(5) = 3: 135|24, 13|25|4, 15|24|3.

%e 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.

%Y Column k=2 of A270953.

%K nonn

%O 5,1

%A _Alois P. Heinz_, Mar 26 2016