*1 = a and x*{n+1} = f(x*n) for all positive integers n. Let d(a) be the smallest n such that x*n = 1. (For example, d(100) = 3 and d(87) = 7.) Let m be the number of positive integers b such that d(b) = 20. Find the sum of the distinct prime factors of m. Source: AOPS

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