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)
(D)
(E) 2
Ans: (A)
想請問這題的意思是不是像
f(2)=1 -->integer是1 -->一個
f(3)=2 -->integers 是 1 和 2 -->二個
f(5)=4 -->integers 是 1, 2, 3, 4 -->四個
所以答案是(A)......?