What are the prime numbers? How to determine whether a number is a prime number?

Prime numbers

Find out whether some integer is a prime number

Is your birth year a prime number? What about your age?

The smallest prime numbers

We give in the following the prime numbers from 0 to 100. There are exactly 25 prime numbers in this list.

2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97

A bit of history…

Although they have been known circa 300 BC, prime numbers remain a mystery of the modern mathematics. It has been known since Ancient history (thanks to the Greek mathematician Euclid) that there exist infinitely many prime numbers; nevertheless, nowadays, it is still difficult to verify the primality of an integer (i.e. to decide whether is a prime number), especially for (very) large integers.

Applications of prime numbers are numerous, both in mathematics and computer science, and include public key cryptography (also referred to as asymmetric cryptography), used in particular for secure payment over the Internet. In fact, the difficulty to decompose a very large number into prime factors (called the prime factorization of an integer) is the basis of the security of many aspects of our digital life (payment by credit card, security of a Web site secured by HTTPS…). This difficulty to perform a prime factorization is especially true for very large numbers, containing hundreds or thousands of digits.

The largest prime number ever exhibited was obtained on 7th January 2016. It is 274 207 281-1. If it was to be written in classical decimal notation, it would be made of… 22 millions of digits! This number is a Mersenne prime, because it is written using the form 2n-1, where n is itself a prime number. This number was obtained thanks to the distributed computer software GIMPS, the goal of which is to discover new prime numbers: this program is a distributed and collaborative software that runs on computers all over the world. GIMPS mainly relies on Lucas–Lehmer primality test for Mersenne primes.

The list of prime numbers

We give below the list of prime numbers from 0 to 50 000 (which include exactly 5 133 prime numbers!).

Another list (here) gives the smallest 1 000 prime numbers.

Is 2017 a prime number?

Yes, 2 017 is a prime number.

Therefore, we currently live a prime year! There are only 14 numerically prime years in the whole 21st century.

The next prime years will be 2 027, 2 029, 2 039, 2 053, 2 063, 2 069, 2 081, 2 083, 2 087, 2 089, and 2 099.