Is a number prime?

Define a function that takes an integer argument and returns a logical value true or false depending on if the integer is a prime.

Per Wikipedia, a prime number ( or a prime ) is a natural number greater than 1 that has no positive divisors other than 1 and itself.

Requirements

• You can assume you will be given an integer input.
• You can not assume that the integer will be only positive. You may be given negative numbers as well ( or 0 ).
• NOTE on performance: There are no fancy optimizations required, but still the most trivial solutions might time out. Numbers go up to 2^31 ( or similar, depending on language ). Looping all the way up to n, or n/2, will be too slow.

Example

IsPrime(1)  /* false */
IsPrime(2)  /* true  */
IsPrime(-1) /* false */