My name is Rob Mathis. I was given this math problem by a friend of mine and it's driving me crazy. I just want to know how to figure it out. The level is probably college level. I am 21 and so is the friend who gave this to me.

Here's the problem.

Find the zip code of a place in a county so that the product of it and the zip code of another place in another county of the same name, but in a different state, is an exact multiple of the number 123456789

The county name that is the same in the different states has four letters.

I have a list of all the zip codes in 4-lettered counties and it would be virtually impossible to multiply them all out, so I think there must be an easier way to do this. Do you have any ideas?

Factorisation into primes: 123456789 = 3*3*3607*3803.

These factors must appear as factors of at least one of the two counties. This should help you to reduce your list considerably.