Hello. My friend asked me to slove a math problem, but i can't slove it too:Find all values of 'n' in this equation: 4^n + 4^(-n) = 14

I'm sure, that n isn't natural number, because:

4^1 + 4^(-1) = 4 + (1/4)^1 = 4 + 1/4 = 4.25

and

4^2 + 4^(-2) = 16 + (1/4)^2 = 16 + 1/16 = 16.0625

14 is greater than 4.25 and is lower than 16.0625, so:

1 < n < 2

I don't have any idea what's next. Can you help me?