In number theory, primality is the property (of a number) of being divisible by only itself and 1. Such a number is called a prime number.

Note: 1 is not prime; instead, it is a unit.


Interesting facts about primes

There are infinitely many prime numbers. All natural numbers greater than or equal to 2 can be expressed uniquely as the product of prime numbers. Such a product is called the prime factorization or prime decomposition of a number.

If a prime number is congruent to 1 (modulo 4), it can be expressed as the sum of two perfect squares; e.g. 5 = 12 + 22, 13 = 22 + 32, 17 = 12 + 42

Not surprisingly, 2 is the only even prime number.

A list of prime numbers less than 100:
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

Pri*mal"i*ty (?), n.

The quality or state of being primal.

[Obs.]

 

© Webster 1913.

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