A322180 The number of permutations of {1,2,...,n,1,2,...,n} with the property that there are k or fewer numbers between the two k's in the set for k=1,...,n.
1, 1, 5, 36, 466, 8942, 240366, 8576860, 392952468, 22470271108
Offset: 0
Examples
In case of n = 2. | permutation --+------------- 1 | [1, 1, 2, 2] 2 | [1, 2, 1, 2] 3 | [2, 1, 1, 2] 4 | [2, 1, 2, 1] 5 | [2, 2, 1, 1]
Extensions
a(9) from Alois P. Heinz, Nov 30 2018