American Roulette: In American Roulette, there are two green zero pockets. This means that there is an additional chance that your wagers will be void. It has a payout of 35/1 if you bet on it, but it essentially doubles the likelihood that all bets will lose money.
So the probability of getting a red on any single spin is 18/37 or 18/38. The probability of getting 13 in a row is (18/37)^13 or (18/38)^13, or 1:11697 or 1:16544 respectively.