As nescio has already stated the odds off picking a number and it landing on it three times in a row are 54871 to 1 against, long odds but better than the odds of winning the lottery.
If you toss a coin the odds are 50% each time to get a head. This is because the coin does not have a memory what went before.
So why should it be any different with a roulette wheel. They are 3 separate events and the roulette wheel does not have a memory. Therefore 1 in 38 three times.
as they would be deemed seperate bets the odds would be about 7 to one each time the wheel spins with bookie as thats the odds on the lotterys of 50 numbers.