; solves the collatz conjecture

; return one step in the sequence
(define (collatz-step n)
  (if (even? n)
    (/ n 2)
    (+ 1 (* 3 n))))

; recurse over all numbers
(define (collatz n)
  (if (= n 1)
    (displayln "All done!")
    (begin
      (display "N = ")
      (displayln n)
      (collatz (collatz-step n)))))

; get input and run it
(displayln "Enter a positive number:")
(collatz (read))