What are the prime numbers less than 14?

Answer 1

We have an ancient Greek mathematician named Eratosthenes to thank for a handy little algorithm for finding the prime numbers in a set. First step: write out all the counting numbers from 2 to the last number in your set: 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14. Start with 2, that's the first Prime number. Second step: cross all the multiples of 2 (after 2) off your list of numbers. That leaves you with: 2, 3, 5, 7, 9, 11, 13. Next step: the next prime in your list is 3. Cross off all the multiples of 3 the same way. There is only one, 9. Now you are left with: 2, 3, 5, 7, 11, 13. The next prime in your list is 5. There are no multiples of 5 to cross off. Besides, 5 squared is 25 and that's larger than 14, so you know you're done. What's left is a list of the prime numbers less than 14: 2, 3, 5, 7, 11, 13. Congratulations! You've just done "The Sieve of Eratosthenes." It works great for lists of prime numbers all the way up to 50, or 100 or beyond!