If the given set A has n elements then set A has 2n subsets how many subsets are there in R equals even numbers less than 20?

Hi

Suppose, I found that number of subsets of set S having n elements can be found by using formula 2^n, where n is number of elements of S.

Let S(n) represents number of subsets of set S having n elements.

S(n) = 2^n

S(n+1) = 2^(n+1)