The aim is to find a formula for the question.
For $n=2$ i get $2^{2^n}=16$ possible functions.
This is the solution for a boolean function with 2 attributes:
01) a -> separable 02) b -> separable 03) not a -> separable 04) not b -> separable 05) a and b -> separable 06) a or b -> separable 07) a xor b -> not separable 08) a nand b -> separable 09) a nor b -> separable 10) a xnor b -> not separable 11) (not a) and b -> separable 12) a and (not b) -> separable 13) (not a) or b -> separable 14) a or (not b) -> separable 15) (not a) xor b -> not separable 16) a xor (not b) -> not separable
But what is the formular for n?