Which of the following doesn't belong?

64, 16, 36, 32, 8, 4

I don't understand this at all ... My brain is like everywhere today

36 does not belong in that group because it is the only number that is not a power of 2:

2^2 OR 2 x 2 = 4

2^3 OR 2 x 2 x 2 = 8

2^4 OR 2 x 2 x 2 x 2 = 16

2^5 OR 2 x 2 x 2 x 2 x 2 = 32

2^6 OR 2 x 2 x 2 x 2 x 2 x 2 = 64