### What are the factors of 641?

To find the factors of a number, when there are no obvious ones, first square root that number. In this case, 641 would square root to somewhere between 25 and 26. The next step is to divide 641 by each prime number between 1 and 25 in turn, seeing if it has any divisors. 641 can be shown to have no divisors between 1 and 25, and thus we can conclude it is prime. Therefore…