# A big Fibonacci number

Consider the Fibonacci sequence, defined by the following recursion:

$$F_1=F_2=1, F_{n+2}=F_{n+1}+F_{n}$$

Let $$n=3^{5^{7}}$$. Calculate the remainder of $$F_n$$ divided by $$521$$.

Note: the answer is a nonnegative integer below $$521$$.

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