# Determine if any number is prime

Source: Internet
Author: User

The prime number is also referred to as prime numbers , which is thenumber of natural numbers greater than 1, except 1 and the number itself, which cannot be divisible by other natural numbers (it can also be defined as only 1 and the number itself two factors). If the natural number greater than 1 is not prime, it is called composite.

Use Python to determine whether a number is prime.

The first method is divisible by dividing the number within the number range, the efficiency is very low, when the number is large time-consuming, the code realizes:

`def is_prime (n):    if n = = 2:        return True    if n 2 = = 0 or n <= 1:        return False    sqr = Int (MATH.SQRT (n ) + 1    for divisor in range (3, SQR, 2):        if n% divisor = = 0:            return False    return True`

The second approach is to use algorithms to optimize the entire logic and execution process, filtering out all primes within N, by defining an array, generating n*true elements, and implementing the Code:

`def prime_sieve (n):    sieve_lst = [True] * n    sieve_lst[0] = False              # First and second not a prime number, set to False    sieve_lst[1] = False for              I in range (3, int (MATH.SQRT (n)) +1):        pointer = i                * # # of multiples within n digits, all set to False while        pointer < n:< C8/>sieve_lst[pointer] = False            pointer + = i           primes = [] for    x in range (n):        if sieve_lst[x]:            Primes.append (i)    print primes    return Primesprime_sieve (33) [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31]`

This algorithm comes from thebook "Hacking Secret ciphers with Python"

Determine if any number is prime

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