%N Numbers n such that there is an arrangement of n points in the plane such that no point is on >= n/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.
%A _N. J. A. Sloane_, Nov 30 2000