Would you please give some references concerning the number of indecomposable modules over preprojective algebras of type $A_n$?

More precisely, I need references about the following claim: The number of indecomposable modules over the preprojective algebra of type $A_n$ is:

1. only one for $n=2$,

2. four for $n=3$,

3. $12$ for $n=4$,

4. $40$ for $n=5$, and

5. an infinite number of indecomposable modules for $n\geq6$.