%N Expansion of (1+x^2-x^3)/(1-x)^4.
%C If Y is a 3-subset of an n-set X then, for n>=4, a(n-4) is the number of (n-3)-subsets of X which have no exactly one element in common with Y. - _Milan Janjic_, Dec 28 2007
%H <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (4,-6,4,-1).
%F a(n-3)=binomial(n,3)-3*n+9, n=4,5,6,.... - _Milan Janjic_, Dec 28 2007
%A _N. J. A. Sloane_.