What letters will fill the blank?

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

A series is given, with one term missing. Choose the correct alternative from the given ones that will complete the series.
XIIIII, IXIIII, IIXIII, IIIXII,IIIIXI, ?

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

13, 17, 19, 23, 29, ?

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

470, 465, 460, 455, ?, 445

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

63, 56, 50, 43, 37, 30, ?

A series is given, with one number missing. Choose the correct alternative from the given ones that will complete the series.
6, 18, 54, ? , 486, 1458

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

46, 41, 35, 30, ?, 19, 13

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

1728, 864, 432, 216, ?