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Numbers k such that there is an arrangement of k points in the plane such that no point is on >= k/2 connecting lines.
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%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