A Roulette wheel is numbered from 1 to 36 in Europe.
In 1842 Francois and Louis Blanc added a '0' to the original roulette wheel in order to up the house odds.
When the game became popular in the States, a second zero slot, marked '00', was added. This was also undertaken to increase the house odds yet further.
If you add up all the individual numbers on the roulette wheel, then the total you come to is an ominous, spine-chilling 666! Superstitious punters should perhaps play with some salt in their hand!