разложить на множители: (n+3)^3-(n-3)^3
(n+3)^3-(n-3)^3=(n^3+3*n^2*3+3*n*3^2+3^3)-(n^3-3*n^2*3+3*n*3^2-3^3)=(n^3+9*n^2+27*n+27)-(n^3-9*n^2+27*n-27)=n^3+9*n^2+27*n+27-n^3+9*n^2-27*n+27=18n^2+54=18(n^2+3)
(n+3)^3-(n-3)^3=n^3+9n^2+27n+27-n^3+9n^2-27n+27=18n^2+54=18*(n^2+3)