Given numbers $n$ and $k$.

Let $[n]$ be the set of all numbers from $1$ to $n$.

A set $A$ is a subset of $B$ if for every $a\in A$, $a$ also belongs to $B$. The empty set ($\emptyset$) is a subset of any set.

It is necessary to find the value of the function $f([n],k)$.

$f([n],1)$ returns the number of subsets in the set $[n]$.

$f([n],k)$ where $k>1$ returns the sum $f(s,k-1)$ where $s$ is a subset of $[n]$.