# How many functions have an n-bit input and m-bit output?

How many functions have an n-bit input and m-bit output?

The first question was how many functions have an n-bit input and a 1 bit (yes/no) output. I thought the answer was $2^{2^n}$, because there were $2^n$ possible inputs, and for each input half the functions would print $1$ on it and half the functions would print $0$.

So the answer to the second question was maybe $(2^{2^n})^m=2^{{2^n}m}$ because it was constructed of m 1-bit functions. Is this correct? Thanks.

$(2^{2^n})^m=2^{{2^n}m}$ is correct through I would take a slightly different approach
The number of functions with $a$ inputs and $b$ possible outputs such as $\{0,1,2,3,\ldots,a-1\} \to \{0,1,2,3,\ldots,b-1\}$ is $b^a$
Here $b=2^m$ and $a=2^n$, so the answer is $\left(2^m\right)^{\left(2^n\right)}$ and that is $2^{{2^n}m}$ as you have