Q: How did you learn to factorize big numbers (>1000) in your head? Could you teach me how to do it?
A: only 1 step at a time. first, i'll tell you how to figure out if a number is even (divisible by 2). if the last digit is even, then the whole number is even. If it's even, divide it by 2, and set the 2 aside as one of the factors for your final answer. to divide a number by 2, try to separate the digits into groups that form numbers you already know how to divide by 2. for example, if you have 1634, ... you can split that into 16 and 34 next to each other. you can safely half each of those, side by side, and keep them next to each other. This is assuming that you already happen to know what 16 divided by 2 is, and what 34 divided by 2 is. If you didn't, then i will go back a couple of steps and just tell you the simple fact that 16 divided by 2 is 8 and 34 divided by 2 is 17. hopefully you can remember that. So you can conclude that 1634 divided by 2 is 817. I got carried away and gave you more like 13 steps instead of 1. i'll try to give fewer steps next time, but i promise to give you all the steps i know, if you want to know them. i apologize if you already knew all of those steps. in case you were looking for something more advanced, i can tell you that 2001 is an awesome checker for both 23 and 29 at the same time