Find a formula for the general term `a_n` of the sequence assuming the pattern of the first few terms continues.

`{ 9,  9/4, 9/16, 9/64, 9/256, \ cdots}`

Assume the first term is `a_1`

`a_n` =  

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Box 1: Enter your answer as an expression. Example: 3x^2+1, x/5, (a+b)/c
Be sure your variables match those in the question