New $(n,r)$-arcs in $\mathrm{PG}(2,17)$, $\mathrm{PG}(2,19)$, and $\mathrm{PG}(2,23)$

An $(n,r)$-arc is a set of $n$ points of a projective plane such that some $r$ but no $r+1$ of them are collinear. The maximum size of an $(n,r)$-arc in $\mathrm{PG}(2,q)$ is denoted by $m_r(2,q)$. In this paper a new $(95,7)$-arc, $(183,12)$-arc, and $(205,13)$-arc in $\mathrm{PG}(2,17)$ are constructed, as well as a $(243,14)$-arc and $(264,15)$-arc in $\mathrm{PG}(2,19)$. Likewise, good large $(n,r)$-arcs in $\mathrm{PG}(2,23)$ are constructed and a table with bounds on $m_r(2,23)$ is presented. In this way many new 3-dimensional Griesmer codes are obtained. The results are obtained by nonexhaustive local computer search.