Generalized outerplanar Tur\'an number of short paths

Let H be a graph. The generalized outerplanar Turán number of H, denoted by fOP(n,H), is the maximum number of copies of H in an n-vertex outerplanar graph. Let Pk be the path on k vertices. In this paper we give an exact value of fOP(n, P4) and a best asymptotic value of fOP(n, P5). Moreover, we characterize all outerplanar graphs containing fOP(n, P4) copies of P4.