Prime numbers are whole numbers greater than 1 that are not divisible by any whole number other than 1 and itself. The first few are 2, 3, 5, 7, 11, 13 … To explain how the RSA algorithm works ...

If the result is not a multiple of 10, then the credit card number is invalid. I’ll show the Luhn algorithm in action on my Visa, but you should try it with your credit card, too.

How to subtract numbers in a single cell in Excel Standard subtraction in Excel is relatively simple. Click in an empty cell, type an equal sign and then enter the numbers you want to subtract.

Find out about the column method to subtract more than 4-digit numbers with this Year 5 article from BBC Bitesize.