# Scientists Say: Prime number

Prime numbers are special because they can be divided only by themselves and one

#### Prime number (noun, “PRYM NUM-ber”)

A prime number is a number can be cleanly divided only by itself and 1.

For instance, 2 and 3 are prime numbers. If you try dividing them by a number other than themselves or one, you’ll get a fraction. But 4 is not a prime number because it can be divided by 2. The next prime number is 5. But 6 is not prime, because it can be divided by 2 and 3. The next several prime numbers are: 7, 11, 13, 17, 19, 23 and 29.

There are infinitely many prime numbers. But they get rarer as numbers get bigger. It’s also harder to check if bigger numbers are prime. As a result, finding increasingly large prime numbers requires a lot of computing power. The largest prime number discovered so far is nearly 25 million digits long.

People have been fascinated by prime numbers at least since the time of ancient Greece. After all, prime numbers can be multiplied together to create all other whole numbers. That makes primes sort of like the building blocks of all whole numbers.

But prime numbers also have practical uses. One of the most important is in encryption. This is the process of hiding private information handled by computers. Prime numbers are key ingredients for the encryption systems that guard credit card information sent over the internet and bank account data at ATMs.

#### In a sentence

Prime numbers are so special that if intelligent aliens exist, scientists think those creatures might use prime numbers to signal us.