Possible Duplicate:
$\{a_{n}\}$ diverges to $+\infty$
Let $ a_ {n} $ a sequence such that $ a_ {n + 1} = 2 ^ {a_ {n}} $, $ a_ {1} = 1 $. Show that $ a_ {n} $ diverges at $ \infty $
My attempt:
Show that is growing by induction
1) $ a_{1}, a_{2}=2$, $a_{1} 2) We assume that $ a_ {n-1}