%I #10 Aug 04 2021 01:48:48
%S 9,15,19,25,31,37
%N Numbers k such that there is an arrangement of k points in the plane such that no point is on >= k/2 connecting lines.
%C Counterexamples to a conjecture of Dirac.
%D H. T. Croft, K. J. Falconer and R. K. Guy, Unsolved Problems in Geometry, F12.
%K nonn,nice,hard,more
%O 1,1
%A _N. J. A. Sloane_, Nov 30 2000