The missing number in the sequence can be determined by subtracting the first number from the second number, and then adding the result to the second number. In this case, (29 - 26) + 29 = 32, (36 - 32) + 36 = 40, and (41 - 36) + 41 = 46. Therefore, the missing number is obtained by subtracting 33 from 36 and adding the result to 36, which is 36 - 33 + 36 = 39. However, since this option is not given, the closest option is 18, which is obtained by subtracting 33 from 26 and adding the result to 26, which is 26 - 33 + 26 = 19. Therefore, the correct answer is 18.