Try the Sieve of Erathosthenes again to help you practice skip-counting by 2's, 3's etc. and to help you better understand factors, multiples, prime and composite numbers. Remember: circle the first prime number (2), then count by 2's and cross off all the multiples of 2. Then circle the next prime number (3). Count by 3's and cross off all the multiples of 3. Keep doing this (circle primes & cross off multiples) and see what remains! Finally, comment on any patterns you notice.