If the generating function for ana_nan is A(x)=1(1−x)3A(x) = \frac{1}{(1-x)^3}A(x)=(1−x)31, find ana_nan.
(n+22)\binom{n+2}{2}(2n+2)
(n+33)\binom{n+3}{3}(3n+3)
n2n^2n2
n(n+1)2\frac{n(n+1)}{2}2n(n+1)