prime numbers

[astral_travel]

Sorry, I gave bad advice. The test for == 2 should be done first. Then I can add a test for even that makes it easier to only test odd factors.

I would write like this:

while True:
    user_input = int(input("Enter Number "))



    if user_input == 2:   # Test first
        print("is prime")
    # No number < 2 is prime.  No even number, other than 2, is prime.
    # Doing this test 2nd lets me report that 2 is prime.
    elif user_input < 2 or user_input & 1 == 0: 
        print("is not prime")
    else:
        # Test all odd numbers between 3 and square_root(user_input)
        for x in range(3, int(user_input**0.5)+1, 2):
            if user_input % x == 0:
                print('is not prime')
                break  # Found a factor.  No reason to test any more factors
        else:
            # If no factor found, must be prime
            print("is prime")

i didn't get why in the line for x in range(3, int(user_input**0.5)+1, 2): there is +1 ...