[tex]a=2^{n+3}\times3^{2n}+2^n\times9^{n+1}+2^n\times3^{2n+1}=\\\\
=2^{n+3}\times (3^2)^n+2^n\times 9^{n+1}+2^n\times(3^2)^n\times3^1=\\\\
=2^n\times2^3\times9^n+2^n\times9^n\times9^1+2^n\times9^n\times 3^1=\\\\
=(2\times9)^n\times2^3+(2\times9)^n\times9^1+(2\times9)^n\times3^1=\\\\
=18^n\times8+18^n\times9+18^n\times3=\\\\
=18^n(8 +9+3)=18^n\times20=\boxed{18^n\times2\times10}\\\\
\texttt{Calculam ultima cifra: } \\ \\
U(18^n \times 2 \times 10) = \boxed{0}~~\text{deoarece unul din factori = 10}[/tex]
