What letters will fill the blank?

Z, X, V, T, R, __,__

In the following question, select the missing number from the given series.
1, 3, 6, 11, 18, ?

In the following question, select the missing number from the given series.
9, 18, 72, 576, ?

In the following question, select the missing number from the given series.

54, 51, 48, 45, 42, ?

In the following question, select the missing number from the given series.
19, 11, 13, 16, 15, 17, 13, 19, 21, ?

In the following question, select the missing number from the given series.
5, 13, 40, 104, ?

What should come in place of the question mark (?) in the following number series? 1, 3, 24, 360,8640, 302400, ?

What will come in place of the question mark (?) in the following number series?14, 18, 9, 25, 0, ?