#-(and) "

P34 (**) Calculate Euler's totient function phi(m).
    Euler's so-called totient function phi(m) is defined as the number
    of positive integers r (1 <= r < m) that are coprime to m.

    Example: m = 10: r = 1,3,7,9; thus phi(m) = 4. Note the special case: phi(1) = 1.

    * (totient-phi 10)
    4

    Find out what the value of phi(m) is if m is a prime
    number. Euler's totient function plays an important role in one of
    the most widely used public key cryptography methods (RSA). In
    this exercise you should use the most primitive method to
    calculate this function (there are smarter ways that we shall
    discuss later).
"

(defun totient-phi (m)
  (loop
     :for r :from 1 :below m
     :when (coprime r m)
     :count 1))

;;;; THE END ;;;;
ViewGit