%I #10 Nov 28 2018 08:01:15

%S 0,1,2,4,8,16,30,56,102,186,336,606,1088,1954,3502,6278,11246,20148,

%T 36086,64640,115774,207374,371430,665298,1191646,2134454,3823160,

%U 6847974,12265912,21970470,39353006,70488334,126257182,226149314

%N Number of j-sets in symmetric group S_n.

%C For a permutation p=p_1 p_2...p_n in S_n and a positive integer i<= n, we can view p_1 p_2...p_i as an element of S_i by order-preserving relabeling. The j-set of p is the set of i's such that p_1 p_2...p_i is an involution in S_i.

%H Christopher Coscia, Jonathan DeWitt, <a href="http://www.combinatorics.org/ojs/index.php/eljc/article/view/v23i2p10/0">Locally Convex Words and Permutations</a>, Electronic Journal of Combinatorics. 23 (2), 2016, #P2.10.

%H Dongsu Kim and Jang Soo Kim, <a href="http://www.combinatorics.org/ojs/index.php/eljc/article/view/v14i1r2">The Initial Involution Patterns of Permutations</a>, Electron. J. Combin., Vol. 14 (1) (2007), #R2.

%F Kim and Kim give a g.f.

%K nonn

%O 1,3

%A _N. J. A. Sloane_, Jan 03 2007

%E More terms from _Vladeta Jovovic_, Jan 03 2007