How to store random generated numbers in a text file? (Python)

I am struggling a bit here with saving the information from the random number generator to a text file.

My code is generating a random number in a certain range, for ever or until the program is terminated. I want to store those numbers in a txt file that I can later open and look at the results.

from random import randint
import time


with open('randnum.txt', 'w') as f:
    f.write(""""I AM STRUGLING WITH WHAT GOES HERE"""")

def roll_many(n,x):
    for i in range(x):
        roll = randint(45000000,45999999)
        print(roll)

roll_many(1,1)
time.sleep(1)

while True:
    roll_many(1,1)
    time.sleep(1)


"""THERE SHOULD ALSO BE SOMETHING HERE TO END THE WRITING?"""