(n+2)!(n^2-9)/(n+4)!
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(n+2)!(n^2-9)/(n+4)! =
=(n+2)! (n^2-9) / (n+2)! (n+3)(n+4)=
=(n-3)(n+3) / (n+3)(n+4)=
=(n-3)/ (n+4)