# isprime.py - find factors of numbers

### By aboutscript on Jan 05, 2013

Find out if a number is prime. If it isn't, you'll get a list of factors. It's useful for finding GCM and other miscellaneous things about numbers.

For example, I was making a 1280x720 picture and I needed to know how it could be broken into squares.

``````\$ ./isprime.py
Number: 1280
[2, 4, 5, 8, 10, 16, 20, 32, 40, 64, 80, 128, 160, 256, 320]
Number: 720
[2, 3, 4, 5, 6, 8, 9, 10, 12, 15, 16, 18, 20, 24, 30, 36, 40, 45, 48, 60, 72, 80, 90, 120, 144, 180, 240]
``````

Now I know it can be divided by 80 each way; and with a little division and then a little multiplication, 1280x720 can be made of 144 80x80 squares. Maybe you don't run into things like this every day, but I do :-)

``````#!/usr/bin/env python

def isprime(n):
return [x for x in range(2, n / 2) if n % x == 0] or False

if __name__ == '__main__':
while True:
n = input('Number: ')
print isprime(n)
``````

Conscious   -  Jan 05, 2013

If you're listing factors, you should also list 1 and n, to be complete
edit: also, shouldn't the 1280 one be returning 640 too?

BlueThen   -  Jan 05, 2013

Should line 4 be returning True if the number has no known multiples?

Hawkee   -  Jan 05, 2013

Much better. Although I'd give it a more descriptive title. It'll draw more people.

Hawkee  -  Jan 06, 2013

There you go. You should be able to pick up more search traffic that way.

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