Fastest way of calculating Prime Number with less system overhead with C code.

A number is said to be a prime number if it is divisible only by 1 and the number itself. That is prime number is divisible by exactly two numbers. For example, 11 is prime number because it is divisible by 1 and 11 itself but 4 is not prime number because it is divisible by 1, 2 and 4.

Test of prime number is famous question in programming. You are supplied any arbitrary number and you have to find out whether it is prime or not. There are various methods and algorithms for testing the prime number condition. Some methods take less iteration and in turn less overhead and some methods take large iteration and in turn large overhead. I will present you two methods; one uses large number of iterations and another uses drastically reduced number of iterations.