No. The OP means Un = 4U_(n-1) or, even better, .
You will need to better learn how to interpret poor formatting (which is why users are encouraged to learn basic latex).
To the OP:
Nope, it's not exactly how you wrote it. Please take the time to learn some basic latex so that you can format equations more clearly next time. See here: http://www.mathhelpforum.com/math-help/latex-help/