On sizes of complete arcs in PG(2,q)PG(2,q)

New upper bounds on the smallest size t2(2,q)t2(2,q) of a complete arc in the projective plane PG(2,q)PG(2,q) are obtained for 853≤q≤5107853≤q≤5107 and q∈T1∪T2q∈T1∪T2, where T1={173,181,193,229,243,257,271,277,293,343,373,409,443,449,457,461,463,467,479,487,491,499,529,563,569,571,577,587,593,599,601,607,613,617,619,631,641,661,673,677,683,691,709}T1={173,181,193,229,243,257,271,277,293,343,373,409,443,449,457,461,463,467,479,487,491,499,529,563,569,571,577,587,593,599,601,607,613,617,619,631,641,661,673,677,683,691,709}, and T2={5119,5147,5153,5209,5231,5237,5261,5279,5281,5303,5347,5641,5843,6011,8192}T2={5119,5147,5153,5209,5231,5237,5261,5279,5281,5303,5347,5641,5843,6011,8192}. From these new bounds it follows that for q≤2593q≤2593 and q=2693,2753q=2693,2753, the relation t2(2,q)<4.5q holds. Also, for q≤5107q≤5107 we have t2(2,q)<4.79q. It is shown that for 23≤q≤510723≤q≤5107 and q∈T2∪{214,215,218}q∈T2∪{214,215,218}, the inequality t2(2,q)2063q>2063. New sizes of complete arcs in PG(2,q)PG(2,q) are presented for 169≤q≤349169≤q≤349 and q=1013,2003q=1013,2003.

► The projective planes PG(2,q)PG(2,q) with q≤5107q≤5107 have been considered.
► We obtain upper bounds on the smallest size of a complete arc in the plane.
► A computer search with randomized greedy algorithms is used.
► We propose a simple formula that describes the experimental results.
► New constructions of families of complete arcs are given.