Hi,

I hope it is the right place to post it...

I need help with the following sequence:

$\displaystyle \sum_{i=0}^{j}2^{2^i}=N$

(it's 2 to the power of 2 to the power of i)

I need to find i as a function of N.

meaning how further away in the sequence do i need to go, in order to get N.

any help would greatly appreciated.