abstract: We consider the Lane-Emden problem
−∆u=
u
p−1u in Ω,
u=0 on ∂Ω,
where Ω ⊂ R2 is a smooth bounded domain. When the exponent p is large, the existence and multiplicity of solutions strongly depend on the geometric properties of the domain, which also deeply affect their qualitative behaviour. Remarkably, a wide variety of solutions, both positive and sign-changing, have been found when p is sufficiently large. In this talk, we focus on this topic and find new sign-changing solutions that exhibit an unexpected concentration phenomenon as p approaches +∞.