Problem #9

Recall that a permutation p on the set {1,2,...,n} is a function p from {1,2,...,n} to itself such that no two elements are mapped to the same element. Call a permutation p an equidistance permutation if there is a constant c such that |p(i) - i| = c for all i in {1,2,...,n}. Find the number of equidistance permutations for n = 1000000.

Source: Weixuan Li and Edward T.H. Wang

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