Starting from 1,297 you write down its successor, then the successor of that, and keep going until you have written 5 numbers in all. What is the last number you write?

Natural numbers (1, 2, 3, …) answer 'how many?' when there is at least one of something. But what if there are none? You need a number for that — and that number is zero. Adding 0 to the natural numbers gives the whole numbers: 0, 1, 2, 3, …. Every whole number sits at a fixed point on the number line, and they never run out — for any whole number you pick, there is always a larger one.