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WHAT ARE THE PRIME NUMBERS? PRIME NUMBERS: • Are “building blocks” for the integers: 1,2,3,4,5,6,7,8,… • Integers with only two factors (1 and itself) Examples: 2,3,5,7,11,13,17,19,23,… COMPOSITE NUMBERS • Are integers that are not prime Examples: 4 = 2*2 (has factors 1,2, and 4) 6 = 2*3 14 = 2*7 2007 = 3*3*223 Determine whether the given number is prime or composite. 1) 2) 3) 4) 5) 24 28 5 25 33 CHALLENGE: If x is any integer, then Can 2x-1 ever be a prime number? Explain why? Determine whether the given number is prime or composite. 1) 2) 3) 4) 5) 24 = 2*2*2*3 28 = 2*2*7 5 is prime 25 = 5*5 33 = 3*11 CHALLENGE: If x is any integer, then Can 2x-1 ever be a prime number? YES! x=2 since 22-1 = 3 MERSENNE PRIMES • Primes numbers of the form 2x-1 are called Mersenne primes. x 2x-1 2 3 3 7 5 31 7 127 12 8191 Largest known prime number 32,582,657 2 -1 • It has 9,808,358 digits! • $100,000 prize for first person to find 10 million digit prime number. How big is that? • Compare that to the number of suspected atoms in the universe, a number with around only 80 digits. IMPORTANCE OF PRIME NUMBERS • Encoding and security of document transfers via the internet or other sources • Crucial and ubiquitous to the subject of number theory. Your mom at the internet • Purchasing items, email accounts, bank transactions, and more Are made secure with the help of prime numbers and mathematicians! How do they make it secure? • Let x and y be “large” prime numbers. x*y = LARGE # Mathematicians proved that the size of your prime numbers x and y determines the length of time to break the code. Try this: 7 * 32 * 5 * 7 = 2 • Factor 40320 Wait just a minute… Mathematicians proved that there are infinitely many primes numbers, and they determined ways to find “really large” ones. Multiplying two prime numbers x and y (each having say 201 digits) gives a 402 digit number x*y = LARGE #. It is known that there are about 10400 prime numbers less than our number LARGE #. • In order to factor our number LARGE #, It will take WAY TOO LONG to look through 10400 prime numbers! "My money is safe!” WHAT ARE THE PRIME NUMBERS? Prepared by Mr. Baczkowski for Blythewood Middle School th 8 grade science class “We love science class!!!!!!”