(r^3+w^2n-3)!
nC3/2nC3
=n!/3!(n-3)!/(2n)!/3!(2n-3)!
=n!(2n-3)!/(n-3)!(2n)!
=n(n-1)(n-2)/(2n)(2n-1)(2n-2)
=(n-2)/4(2n-1)