%I #13 Feb 04 2019 14:22:25
%S 1,2,6,20,66,188,466,1022,2098,4032,7342,13090,22726,38824,65286,
%T 108902,179762
%N Let a(n) = the number of permutations (p(1),p(2),p(3)...,p(n)) of (1,2,3,...,n) where, if each (m,p(m)) is plotted on a graph, then the entire set P of the n of these plotted points would be on the perimeter of the convex hull of P.
%C Three points that are consecutive along the perimeter of the convex hull may be along the same line, in some of the permutations that are counted.
%C The first 8 terms were calculated by _W. Edwin Clark_. The first 17 terms were calculated by _Jan Kristian Haugland_, and posted to the Usenet group sci.math.
%e For n=5, (p(1),p(2),p(3),p(4),p(5)) = (1,3,5,2,4) would be included in the count, but (1,4,3,2,5) would not because point (3,3) is not on the perimeter of the convex hull of P.
%K more,nonn
%O 1,2
%A _Leroy Quet_, Feb 16 2009