Given natural number $n$, how many multisets are there which sum of their elements equals $n$?
There is a recursive function which can give the value in $O(n^2)$, but is there a formula for that?
$f(n,i)$ = answer where minimum elements of multisets are at least $i$.
$f(n,i) = 1$ for $n=0$
$f(n,i) = 0$ for $i>0$
$f(n,i) = f(n,i+1) + f(n-i,i)$ for $ 0 < i \le n$