Maximal (n,3)-arcs in PG(2,11)

In this paper we determine the largest size of a complete (n,3)-arc in PG(2,11). By a computer-based exhaustive search that exploits the fact that an (n,3)-arc with n⩾21 contains an arc of size 7 and that uses projective equivalence properties, we show that the largest size of an (n,3)-arc in PG(2,11) is 21 and that only two non-equivalent (21,3)-arcs exist.