“I discovered a way of colouring the natural numbers that I have found very fascinating. I use following eight colours: black, red, green, yellow, blue, magenta, cyan and white. It started years ago when I realised that those numbers that can be expressed as the sum of just two squares (1, 2, 4, 5, 8, 9, 10, 13 etc.) contain all their multiplication products (e.g., 2×5=10)…”