2014-07-27T10:57:42+08:00
A prime number (or a prime) is a natural number greater than 1 that has no positive divisors other than 1 and itself. A natural number greater than 1 that is not a prime number is called a composite number.
For example, 5 is prime because 1 and 5 are its only positive integer factors, whereas 6 is composite because it has the divisors 2 and 3 in addition to 1 and 6. The fundamental theorem of arithmetic establishes the central role of primes in number theory: any integer greater than 1 can be expressed as a product of primes that is unique up to ordering.
The uniqueness in this theorem requires excluding 1 as a prime because one can include arbitrarily many instances of 1 in any factorization, e.g., 3, 1 × 3, 1 × 1 × 3, etc. are all valid factorizations of 3.
The property of being prime (or not) is called primality. A simple but slow method of verifying the primality of a given number n is known as trial division.
It consists of testing whether n is a multiple of any integer between 2 and . Algorithms much more efficient than trial division have been devised to test the primality of large numbers. Particularly fast methods are available for numbers of special forms, such as Mersenne numbers. As of April 2014, the largest known prime number has 17,425,170 decimal digits.

2014-07-27T11:21:49+08:00
A Prime number is a natural number (counting number) that can be divided only by 1 or itself.

Like the numbers; 2,3,5,7,9
3 can only be divided by 1 or itself, hence, it is a prime number.
6, can be divided by 1,2,3, hence, it is NOT a prime number, rather, it is called a composite number

NOTE:
-2 is the only even prime number.
-0 and 1 aren't considered as prime numbers.

that can be divided only by 1 or itself.
A prime number (or a prime) is a natural number greater than 1 that has no positive divisors other than 1 and itself. A natural number greater than 1 that is not a prime number is called a composite number
13579 and so on