[tex] {2}^{2n + 1} \times {5}^{n} + {4}^{n} \times {5}^{n + 1} [/tex]
[tex] = {2}^{2n + 1} \times {5}^{n} + {2}^{2n} \times {5}^{n + 1} [/tex]
[tex] = {2}^{2n} \times {5}^{n} (2 + 5)[/tex]
[tex] = {2}^{2n} \times {5}^{n} \times 7 \: \: \: \vdots \: \: \: 7[/tex]