What is log4(256)

We are asking "how many 4's need to be multiplied together to get 256?"
4 × 4 × 4 × 4 = 256, so we need 4 of the 4's
So log4(256) = 4
I found an answer from www.slac.stanford.edu
The three-loop on-shell renormalization of QCD and QED
677. 256. 33. 4 3 + 3 2 log 2. 2 log2 2. 55. 32. 2 +. 7. 40. 4. 1. 2. log4 2 12a4. ;. d(2 ). 2. = 11. 32"2. 91. 64". 605. 128. +. 3. 8 3. 1. 4. 2 log 2 +. 1. 12. 2. +". 3799. 256.
For more information, see The three-loop on-shell renormalization of QCD and QED
I found an answer from functions.wolfram.com
ArithmeticGeometricMean
2 log4 logb. Π logb. 4. 1 b2. 8 log4 logb. 2 b4 Π 40 log2. 2 log1024 5 logb log256 2 logb. 1 8. 256 log4 logb. 3 b6 Π 4 log2 log2 23 132 log2 27 logb 792 log. 2.
For more information, see ArithmeticGeometricMean