Problem - 3191
Prove that $7\mid 8^n-1$ for $n\ge 1$.
Because $8^n -1 \equiv 1^n -1 \equiv 0\pmod{7}$, therefore the conclusion holds.
Prove that $7\mid 8^n-1$ for $n\ge 1$.
Because $8^n -1 \equiv 1^n -1 \equiv 0\pmod{7}$, therefore the conclusion holds.