IIN that I don't understand prime numbers?

To find out if a number is prime all you need to do is find the square root of the nearest square number, then check if any numbers up to that root number go into your number, if not then the number you are checking is prime example: if you wanted to find out if 61 is prime the nearest square number is 64 (8X8=64) so 8 is the square root of 64 so you check all numbers up to 8
ignore 1 it doesn't count
2,4,6 & 8 are all even you can't divide an even into an odd
It doesn't end in 0 or 5 so can't be divided by 5
The components of the original number (6 & 1) don't add up to a number in the 3 times table so 3 doesn't go either
you only got to check the number 7
If you know your tables you will know 61 is not in 7 times table
Therefore 61 is prime.
Easy