Given the geometric sequence: 13, 7811, 468121, \displaystyle {13},\ \frac{{78}}{{11}},\ \frac{{468}}{{121}},\ \cdots

Find an explicit formula for an\displaystyle {a}_{{n}}, where the first term is a1=13\displaystyle {a}_{{1}}={13}.
an=\displaystyle {a}_{{n}}=  

Find a7=\displaystyle {a}_{{{7}}}=