%I
%S 0,1,5,15,42,94,189,340,572,903,1365,1981,2790,3820,5117,6714,8664,
%T 11005,13797,17083,20930,25386,30525,36400,43092,50659,59189,68745,
%U 79422,91288,104445,118966,134960,152505,171717,192679,215514,240310,267197,296268,327660
%N Number of pairs of intersecting diagonals in the interior and exterior of a regular ngon.
%H Eric Weisstein, <a href="http://mathworld.wolfram.com/RegularPolygonDivisionbyDiagonals.html">Regular Polygon Division by Diagonals</a> (MathWorld).
%H <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>, signature (3,1,5,5,1,3,1).
%F a(n) = 1/8*n*(n^311*n^2+43*n58) for n even;
%F a(n) = 1/8*n*(n3)*(n^28*n+19) for n odd.
%F a(n) = A176145(n)  A211379(n).
%F G.f.: x^4*(2*x^53*x^47*x^3x^22*x1) / ((x1)^5*(x+1)^2). [_Colin Barker_, Feb 14 2013]
%p a:=n>piecewise(n mod 2 = 0,1/8*n*(n^311*n^2+43*n58),n mod 2 = 1,1/8*n*(n3)*(n^28*n+19),0);
%Y Cf. A176145, A211379.
%K nonn,easy
%O 3,3
%A _Martin Renner_, Feb 07 2013
