The Hilbert series of the preprojective algebras

The aim of this short note is to prove the formula of the Hilbert series of the preprojective algebras in arbitrary characteristic by making effective use of the formulas of the Hilbert series of differential graded (dg) algebras with Adams grading. We also compute the Hilbert series of the quiver Heisenberg algebras, a special class of central extensions of preprojective algebras.