Find an explicit formula for the geometric sequence 3\,,\,15\,,\,75\,,\,375,...3,15,75,375,...3, comma, 15, comma, 75, comma, 375, comma, point, point, point.
Note: the first term should be \textit{a(1)}a(1)start text, a, left parenthesis, 1, right parenthesis, end text.
a(n)=a(n)=a, left parenthesis, n, right parenthesis, equals