# Programmer: Sriram Pemmaraju # Date: Feb 20, 2015 # This program reads a positive integer N and lists all twin # prime pairs (x, x+2) such that x+2 <= N. import math N = int(input("Please type a positive integer: ")) n = 3 # n will take on odd values from 3 through N # variable to remember if the previously processed number is a prime previousPrime = False while n <= N: factor = 2 # initial value of possible factor isPrime = True # variable to remember if n is a prime or not factorUpperBound = math.sqrt(n) # the largest possible factor we need to test is sqrt(n) # loop to generate and test all possible factors while (factor <= factorUpperBound): # test if n is evenly divisible by factor if (n % factor == 0): isPrime = False break factor = factor + 1 # Output if isPrime and previousPrime: print(n-2, n) # Update previous prime and move n to the next odd value previousPrime = isPrime n = n + 2