In the following question, select the missing number from the given series. 1, 3, 7, 15, 31, ?

Refer to the following letter series and answer the question. (Counting is to be done from left to right only). (Left) Z M L Q B X K C H A W V N T R Y D F J P I A U K E O X Z (Right) How many such vowels are there, each of which is immediately preceded by a vowel and immediately followed by a vowel?

Refer to the following number and symbol series and answer the question. Counting is to be done from left to right only. (All numbers are single-digit numbers only). (Left) 2 ^ 7 ? $ % < ? 4 3 \ & * @ # < 6 7 + 3 # (Right) How many such numbers are there, each of which is immediately preceded by a symbol and also immediately followed by a symbol?