Find the missing number in the sequence: 8, 13, 20,?, 40, 53.

Explanation

Look at the successive differences: 13 − 8 = 5 and 20 − 13 = 7. The differences increase through consecutive odd numbers: 5, 7, 9, 11, 13. Therefore, 20 + 9 = 29, 29 + 11 = 40, and 40 + 13 = 53. So the missing number is 29.