Cyclopropeniumyl cation is cyclic, planar, each C atom is sp2 hybridized and there are 2 pi-electrons. This cation is aromatic according to the (4N+2) Hueckel rule with N=0. Note that the Hueckel rule has to do with the number of electrons; the Hueckel rule says that cyclopropeniumyl cation, C3H3+ and cyclobutadiene dication, C4H42+, both are aromatic with 2 pi-electrons.