The mean of the coefficients of $\mathrm{x},{\mathrm{x}}^2,....,{\mathrm{x}}^7$ in the binomial expansion of ${(2+\mathrm{x})}^9$ is _______

$\mathrm{E}\equiv {(2+\mathrm{x})}^9$
$$\begin{gathered} =9{\mathrm{c}}_0{2}^9{\mathrm{x}}^0+9{\mathrm{c}}_1{2}^8{\mathrm{x}}^1+9{\mathrm{c}}_2{2}^7{\mathrm{x}}^2+9{\mathrm{c}}_3{2}^6{\mathrm{x}}^3+9{\mathrm{c}}_4{2}^5{\mathrm{x}}^4+9{\mathrm{c}}_5{2}^4{\mathrm{x}}^5+9{\mathrm{c}}_6{2}^3{\mathrm{x}}^6 \\ +9{\mathrm{c}}_7{2}^2{\mathrm{x}}^7+9{\mathrm{c}}_8{2}^1{\mathrm{x}}^8+9{\mathrm{c}}_9{2}^0{\mathrm{x}}^9 \end{gathered}$$
$\therefore$The mean of the coefficients of $\mathrm{x},{\mathrm{x}}^2,....,{\mathrm{x}}^7$ in the binomial expansion of ${(2+\mathrm{x})}^9\mathrm{is}$
$$\begin{gathered} 9{\mathrm{c}}_0{2}^9+9{\mathrm{c}}_1{2}^8+9{\mathrm{c}}_2{2}^7+9{\mathrm{c}}_3{2}^6+9{\mathrm{c}}_4{2}^5+9{\mathrm{c}}_5{2}^4+9{\mathrm{c}}_6{2}^3 \\ \frac{+9{\mathrm{c}}_7{2}^2+9{\mathrm{c}}_8{2}^1+9{\mathrm{c}}_9{2}^0-9{\mathrm{c}}_0{2}^9-9{\mathrm{c}}_8{2}^1-9{\mathrm{c}}_9{2}^0}{7} \end{gathered}$$
$=\frac{3^9-2^9-9\left(2\right)-1}{7} (\because {(\mathrm{x}+1)}^9\mathrm{at}\mathrm{x}=2) =\frac{19152}{7}=2736$