# Prime Number Checker

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 Submitted on: 5/5/2018 5:48:19 PM By: Gaurav Singh Level: Beginner User Rating: Unrated Compatibility: PHP 5.0 Views: 4079

How to Check if a Number is Prime

  A prime number (or a prime) is a natural number greater than 1 that cannot be formed by multiplying two smaller natural numbers. A natural number greater than 1 that is not prime is called a composite number. For example, 5 is prime because the only ways of writing it as a product, 1 × 5 or 5 × 1, involve 5 itself. However, 6 is composite because it is the product of two numbers (2 × 3) that are both smaller than 6. Primes are central in number theory because of the fundamental theorem of arithmetic: every natural number greater than 1 is either a prime itself or can be factorized as a product of primes that is unique up to their order. The property of being prime is called primality. A simple but slow method of checking the primality of a given number n {\displaystyle n} n, called trial division, tests whether n {\displaystyle n} n is a multiple of any integer between 2 and n {\displaystyle {\sqrt {n}}} {\sqrt {n}}. Faster algorithms include the Miller–Rabin primality test, which is fast but has a small chance of error, and the AKS primality test, which always produces the correct answer in polynomial time but is too slow to be practical. Particularly fast methods are available for numbers of special forms, such as Mersenne numbers. As of January 2018, the largest known prime number has 23,249,425 decimal digits. Check if Prime Number Calculator Note : This Prime Number Calculator performs primality test and checks if a positive number is prime. 

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