Multiprocessing: Threads work well. Processes don't work.

[snippsat]

Code works.
Here with added timing and max_workers=8(use 8 cores).
Then it should be easier to see if it work,and run from command line not any editors when this out.

import concurrent.futures
import math, time

PRIMES = [
    111111111191122,
    112582705942171,
    112272535095293,
    115280095190773,
    115797848077099,
    1099726899285419
] * 10 # Longer run time

def is_prime(n):
    if n < 2:
        return False
    if n == 2:
        return True
    if n % 2 == 0:
        return False
    sqrt_n = int(math.floor(math.sqrt(n)))
    for i in range(3, sqrt_n + 1, 2):
        if n % i == 0:
            return False
    return True

def main():
    start = time.time()
    with concurrent.futures.ProcessPoolExecutor(max_workers=8) as executor:
        for number, prime in zip(PRIMES, executor.map(is_prime, PRIMES)):
            print(f'{number} is prime: {prime}')
    stop = time.time()
    total = stop - start
    print(f'Time was: {total:.2f}')

if __name__ == '__main__':
    main()

Output:
.....
115280095190773 is prime: True
115797848077099 is prime: True
1099726899285419 is prime: False
Time was: 6.17

If set max_workers=1 also now use only 1 core in CPU.
The time should be slower.

Output:
.....
115280095190773 is prime: True
115797848077099 is prime: True
1099726899285419 is prime: False
Time was: 23.63