%I A004677
%S A004677 1,1,1,2,11,91,17,323,4807,3289,8671,11687,15283,10743949,
%T A004677 15189721,21069613,1339779509,1339779509,101007559,101007559,
%U A004677 4215217889,185371558793,8059632991,11489264051,815737747621
%N A004677 Numerator of 2^n*(3*n-3)!/( ((n-1)!)^3 * (2*n)! ).
%D A004677 Valtr, Pavel; The probability that $n$ random points in a triangle are 
               in convex position. Combinatorica 16 (1996), no. 4, 567-573.
%H A004677 Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/
               SylvestersFour-PointProblem.html">Link to a section of The World 
               of Mathematics.</a>
%Y A004677 Cf. A000139.
%Y A004677 Sequence in context: A099662 A099693 A138552 this_sequence A094955 A143870 
               A047854
%Y A004677 Adjacent sequences: A004674 A004675 A004676 this_sequence A004678 A004679 
               A004680
%K A004677 nonn
%O A004677 1,4
%A A004677 N. J. A. Sloane (njas(AT)research.att.com).