Find the missing letters :

$2, 10, 30, 68, ?$

Find the missing number :

$31, 35, 43, 59, 91, ?$

Find the missing number :

$3, 1.5, 1.5, 2.25, 4.5, ?$

Find the missing letters:

$1, 2, 6, 24, 120, ?$

Find the missing number :

$34, 18, 10, 6, 4, ?$

Find the missing number :

$2, 5, 9, 19, 37, ?$

Find the missing number.

$14, 50, 110, 200, ?$

Find the missing number.

$1, 2, 5, 12, 27, ?$

Find the missing number.

$17, 19, 23, 29, 31, ?$