Number of key permutations of length n: permutations {a_i} with |a_i-a_{i-1}|=1 or 2.
1, 2, 6, 12, 20, 34, 56, 88, 136, 208, 314, 470, 700, 1038, 1534, 2262, 3330, 4896
1 seqfan posts
Sat Mar 27 20:18:04 CET 2010 [seqfan] permutations p in S_n such that m <= |p(i)-p(i+1)| <=M for i from 1 to n-1.