[tex]5^6 \equiv 1 \mod(7)[/tex]
[tex]\left(5^6\right)^{421} \equiv \left(1\right)^{421} \mod(7)[/tex]
[tex]5^{2526}\equiv 1 \mod(7)[/tex]
[tex]5^{2526}\cdot5^4\equiv 625 \mod(7)[/tex]
[tex]5^{2530}\equiv 625 \mod(7)[/tex]
[tex]5^{2530}\equiv 2 \mod(7)[/tex]
5^2530 dá resto 2 na divisão por 7.
