find coefficients for hashing a sequence

[ofer...@gmail.com]

Given an array of integers A = <a_1..a_n> where a_1..a_n is a permutation of 1..n, I would like to compute a scalar 'signature' of A, sig(A), such that for any two distinct permutations of A, their signatures are different. 
For example, suppose that I compute my signature with a sum
sig(A) = \Sigma_{i=1..n} (i * A[i])
i.e., multiply each element with its idx. This does not work because, e.g., Sig(2,3,1) = Sig(3,1,2).
I can either
1. stay with this signature but find coefficients other than simply the idx. I could not find a way to model in minizinc the problem of finding those coefficients. Any idea ?
2. find a different signature. Any idea ?

[Krzysztof Bordon]

You can use a sequence of increasing prime numbers for this purpose: sig(A) = \Sigma_{i=1..n} (Prime[i] ^ A[i])
where Prime[] = (2, 3, 5, 7, 11, 13, ...). For example, for the permutation A = (2, 3, 1) the Sig(A) would be 2^2 + 3^3 + 5^1 = 4 + 27 + 5 = 36. The signature proves to be different for any different permutation.

Best regards,
KB

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