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%I #3 Sep 13 2003 03:00:00
%S 1,4,3,5,5,6,7,7,8,9,9,10,11,11,12,13,13,14,15,15,16,17,17,18,19,19,
%T 20,21,21,22,23,23,24,25,25,26,27,27,28,29,29,30,31,31,32,33,33,34,35,
%U 35,36,37,37,38,39,39,40,41,41,42,43,43,44,45,45,46,47,47,48,49,49,50
%N Greatest possible number of right angles that can occur as interior angles in a planar n-gon.
%C Reflex angles (e.g. 270 degrees) are not considered right angles. From a(6) on, this duplicates A004396 from its eighth term.
%F a(3) = 1; a(4) = 4; a(5) = 3; a(3*k+3) = 2*k+3; a(3*k+4) = 2*k+3; a(3*k+5) = 2*k+4 where k starts from 1 OR a(n) is the greatest integer less than 2/3*(n+2) where n starts from 6.
%e a(3) = 1 because you can only have one right angle in a triangle; a(4) = 4 as in a rectangular quadrilateral; a(100) = 67 etc.
%Y Cf. A004396.
%K easy,nonn
%O 3,2
%A Deepak R. N (deepak_rama(AT)bigfoot.com)