# Please help me

posted by
**Mathslover** on
.

How many permutations σ of the set {1,2,…,15} are there such that σ(1)=1,∣σ(n)−σ(n−1)∣≤2 for 2≤n≤15?

Details and assumptions

σ(n) denotes the nth position of the permutation.