Number 13 Universally the Unluckiest Number\n\n Said to refer to Judas, who was the 13th disciple and who betrayed Jesus at the Last Supper, number 13 is perhaps one of the least played numbers in any form of betting.
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.