For each integer n 2 let an be the number of permutations
Chapter 9, Problem 28E(choose chapter or problem)
For each integer n ? 2 let an be the number of permutations of {1, 2, 3, ..., n} in which no number is more than one place removed from its “natural” position. Thus a1 = 1 since the one permutation of {1}, namely 1, does not move 1 from its natural position. Also a2 = 2 since neither of the two permutations of {1,2}, namely 12 and 21, moves either number more than one place from its natural position.a. Find a3.________________b. Find a recurrence relation for a1, a2, a3, …
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