The function f is defined for all positive integers n by the following rule: f(n) is the number of positive integers each of which is less than n and has no positive factor in common with n other than 1. If p is any prime number, then f(p) = ?
a) p -1
b) p - 2
c) (p + 1)/2
d) (p - 1)/2
e) 2
a) p -1
b) p - 2
c) (p + 1)/2
d) (p - 1)/2
e) 2
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