# Not quite Graham's number

Number Theory Level 4

Using Knuth's up-arrow notation, we define a sequence $a_{n+1} = 7 \uparrow \uparrow \ldots \uparrow 7$ where there are $$a_{n}$$ arrows, starting with $$a_{0} = 4$$.

Find the last 5 digits of $$a_{64}$$.

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