Simplifying a log of a log I have a summation series that unfortunately involves a log of a log. It looks like the following (assume all log are log base 2): sum_(i=1)^k log log ((n)/2^(k-i)) I'd like to simplify this somehow, such as move the logs or the n value to the outside of the equation, so that I can use the closed form of the geometric series sum to further simplify the equation, but I'm not sure where to start.

Chloe Arnold

Chloe Arnold

Answered question

2022-10-29

Simplifying a log of a log
I have a summation series that unfortunately involves a log of a log. It looks like the following (assume all log are log base 2):
i = 1 k log log n 2 k i
I'd like to simplify this somehow, such as move the logs or the n value to the outside of the equation, so that I can use the closed form of the geometric series sum to further simplify the equation, but I'm not sure where to start.
Thanks for the help!

Answer & Explanation

n8ar1val

n8ar1val

Beginner2022-10-30Added 12 answers

Well, let's see:
i = 0 k 1 log ( log ( n 2 i ) ) = log ( i = 0 k 1 log n + log 2 i ) = log ( i = 0 k 1 log n i ) = log ( k ! ( log n k ) ) = log ( ( log n ) k ) = log ( Γ ( log n + 1 ) Γ ( log n k + 1 ) ) = log ( Γ ( log n + 1 ) ) log ( Γ ( log n k + 1 ) )
Where ( x ) k is the Pochhammer symbol
( x ) k = x ( x 1 ) ( x k + 1 )
We used log a + log b = log ( a b ) and log 2 2 k = k

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