The formula 2^2n-1 denotes the nthe term of a sequence. which term of the sequence is 2^21

a). 11th
b). 6th
c). 10th
d). 8th?

If you meant: 2^(2n-1) , then

2^(2n-1) = 2^21
and 2n-1 = 21
solve for n