Exponents

 81^n=9*27*27*9?

n ==Log[9*27*27*9) / log(81)

n==2.5

Alternatively:

$81^n=9^{2n}$

$9*27*27*9=9*3*9*3*9*9=9^5$

Hence $9^{2n}=9^5$  so $2n=5$  or $n=5/2$