Adam Spencer's Summer by Numbers 8

Eight is a Fibonacci number. Named after the Italian mathematician Fibonacci, or Leonardo of Pisa, the Fibonacci numbers

0, 1, 1, 2, 3, 5, 8, 13 ...

... obey the rule that you add together the last two numbers to get the next one. But for such a simply defined sequence Fibonacci numbers occur in an amazingly wide array of places - from statistics and geometry through to the natural world such as the number of fruitlets on a pineapple or leaves on various stems.

Here's another cool thing about the Fibonacci numbers. Imagine we have a group of chairs and boys and girls who want to sit in them. How many arrangements can we have as long as two boys don't sit next to each other (you know what boys are like!)

What do you notice about the answers 2, 3, 5, 8?

That's right they're the Fibonacci numbers! Why not convince yourself that when you have 5 chairs there are 5 + 8 = 13 ways and just take it from me that with 8 chairs ... there are 55 acceptable seating arrangements?

It often puzzles people that October is actually the 10th month of the year – what with "oct" meaning 8 and all (octagon, octopus and so on). The confusion usually lasts until the person is lucky enough to meet an expert on Roman history, in particular the Roman calendar.

Now to be honest, experts in Roman history can be a little thin on the ground these days, but this is where you come in. Next time someone wonders aloud, "Why is October the 10th month of the year and not the 8th?" you can reply quick as a flash ...