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How to prove $(n+1)! = O(2^{(2^n)})$
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Problem
I am trying to prove $(n+1)! = O(2^{(2^n)})$. I am trying to use L'Hospital rule but I am stuck with infinite derivatives.
Can anyone tell me how i can prove this?
Can anyone tell me how i can prove this?
Solution
Well, since this upper bound is not nearly tight, you can just use basic transformations to get
$$(n+1)!< (n+1)^{n}=2^{\log (n+1)^{n}}= 2^{n\log (n+1)}=O(2^{n\log n})\subset O(2^{(2^n)}). $$
$$(n+1)!< (n+1)^{n}=2^{\log (n+1)^{n}}= 2^{n\log (n+1)}=O(2^{n\log n})\subset O(2^{(2^n)}). $$
Context
StackExchange Computer Science Q#6075, answer score: 12
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