What number is next (right) to the number ‘20’ on a standard British dart board?

For the sake of clarity, here’s how a modern, conventional dartboard’s numbers are structured, starting at the top and working clockwise: 20, 1, 18, 4, 13, 6, 10, 15, 2, 17, 3, 19, 7, 16, 8, 11, 14, 9, 12, 5.