How to find a prime number using python [duplicate]

Question

I have developed a code to find a prime number using python. But it keeps saying the numbers are prime even tho they are not. I am new to python so my knowledge in syntax is really not as good

when i input the number 15 it would say it is a prime number. but it shouldn't be a prime number

a = 0
#num will be the number we are checking
x = int(num)
num = sqrt(float(num))
num = int(num)
primeCheck = True
for a in range(3, num, 2):
    if x == 1 or x == 2:
        primeCheck = False
        #not prime
    if x % a == 0:
        primeCheck = False
        #not prime
if primeCheck == true:
    #prime

There are many answers in SO about that, why don't you check those before asking again? — c0x6a
– c0x6a, Commented Jun 16, 2019 at 19:40

Draconis · Accepted Answer · 2019-06-16 19:34:41Z

0

You want x % a, not a % x. The larger number should almost always be on the left for the mod operation.

answered Jun 16, 2019 at 19:34

Draconis

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