''' recursively pushes the prime factors of the int on the top of the stack'''
PROC factors
  ''' only proceed if the input is valid '''
  IF DUP 1 < DO
    ''' find the smallest number that divides n '''
    2 WHILE OVER OVER SWAP % 0 != DO 1 + END
    ''' print it and find the next factor '''
    DUP PUT " " PUT
    OVER OVER SWAP / factors
  ELSE
    "" PUTLN
  END
END

PROC MAIN
  "Prime factors of 12:" PUTLN 12 factors
  "Prime factors of 5:"  PUTLN 5  factors
  "Prime factors of 60:" PUTLN 60 factors
  "Prime factors of 97:" PUTLN 97 factors
END