Which number will replace the question mark (?) in the following series? 2, 7,…

Find the differences between consecutive terms of the series:

7 − 2 = 5
14 − 7 = 7
23 − 14 = 9
? − 23 = 11 → ? = 23 + 11 = 34
47 − 34 = 13

The differences are consecutive odd numbers: +5, +7, +9, +11, +13. Adding 11 to 23 gives the missing term, 34.