Exponents

$2^{10} = 2^{10}$

$4^{20} = 2^{2^{20}} = 2^{40}$

$8^{40} = 2^{2^{2^{40}}} = 2^{160}$

$2^{10} * 2^{40} * 2^{160} = 2^{210}$

So... $n = 210$

I agree with Bs answer until  8⁴⁰  =  (2³)⁴⁰  =  120