%I #14 Oct 09 2021 16:02:27
%S 0,0,2,4,6,9,11,14,18,20
%N Maximum over all sets of n points in the plane of the number of second-smallest distances between the points.
%H Peter Brass, <a href="https://doi.org/10.1007/BF02187849">The maximum number of second smallest distances in finite planar sets</a>, Discrete & Computational Geometry 7.1 (1992): 371-379.
%H Peter Brass, <a href="/A293956/a293956.png">Annotated version of Fig. 1 from Brass (1992)</a>, illustrating small values of a(n).
%Y Cf. A047932, A186705.
%K nonn,more
%O 1,3
%A _N. J. A. Sloane_, Nov 01 2017