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Questions related to permutations, bijections from a finite (or sometimes infinite) set to itself.

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Permutations which avoid consecutive entries of the form (m,m+1)

I've just started understanding permutations but could not understand as to how I can come up with a general formula for this problem. Consider all permutations of the numbers 1 to n. … For a given n, count the number of good permutations. For example, for n = 3, the good permutations are: 1, 3, 2 2, 1, 3 3, 2, 1 Come up with a form of an answer which can be easily calculated. …