It does some nifty expansions like:
calling a= 5x and b =2
So numbers like 15617 which equal 25^3 - 2^3 can be factored but not always into primes.
15617 = (23)(679)
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
A number by itself is useful, but it is far more useful to know how accurate or certain that number is.