#75
Euler's Totient Function
| Difficulty: | Medium |
| Topics: |
Two numbers are coprime if their
greatest common divisor equals 1.
Euler's totient function f(x) is defined as
the number of positive integers less than x which are coprime to x.
The special case f(1) equals 1.
Write a function which calculates Euler's totient function.
 | (= (__ 1) 1) |
| (= (__ 10) (count '(1 3 7 9)) 4) |
| (= (__ 40) 16) |
| (= (__ 99) 60) |