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%I #3 Mar 31 2012 13:22:18
%S 1,5,15,31,60,108,171,264,396,556,770,1050,1375,1785,2295,2880,3600,
%T 4425,5395
%N Maximum number of trapezoids that can be formed by n lines in plane.
%K nonn
%O 4,2
%A _Erich Friedman_