Question 84
Prove that if $a$ is an integer relatively prime with $35$ then
$$
\left(a^{4}-1\right)\left(a^{4}+15 a^{2}+1\right) \equiv 0 \quad \bmod 35
$$
$$
\left(a^{4}-1\right)\left(a^{4}+15 a^{2}+1\right) \equiv 0 \quad \bmod 35
$$
MathNet 2013 Question 84
Math Olympiad Vault · MathNet 2013