Amicable Numbers

In the world of numbers, 220 and 284 are special because they come as a pair.

They are a pair because, if you take all the numbers that divide 220 (1, 2, 4, 5, 10, 11, 20, 22, 44, 55, 110 – but not 220 itself) and add them together you get 284.

However, if you take all the numbers that divide 284 (1, 2, 4, 71, 142 – but not 284 itself) and add them together, you get 220.

These are called Amicable Numbers, and in ancient times these numbers represented mutual harmony, perfect friendship and love.

From http://mathsgear.co.uk/products/amicable-numbers-pair-of-keyrings-nerd-romance