Four positions of such a sequence are given to be 3s, and we have 10 choices for the remaining eight positions. So the number of such sequences is

or 100 million.
Answer:
D. 9 ÷ 2
Step-by-step explanation:
For getting the nth value of the sequence we simply put the value of n in a formula.
In the given sequence for finding the 5th term we simply put n = 5 in given explicit formula:
We have 
Putting n = 5

⇒ 
⇒ 
Thus, option (D) is correct.