Source: 2014 Saudi Arabia Pre-TST 2.1
Tags: number theory, divides, divisible
Prove that $2014$ divides $53n^{55}- 57n^{53} + 4n$ for all integer $n$.
$2014=2\cdot19\cdot 3$
$53n^{55}-57n^{53}+4n\equiv 53n-57n\equiv 0\pmod 2$
$53n^{55}-57n^{53}+4n\equiv 15(n^{19})^2\cdot n^{17}-0\cdot n^{53}+4n\equiv 15n^{17}+4n\equiv 19n\equiv 0\pmod {19}$
$53n^{55}-57n^{53}+4n\equiv 0\cdot n^{55}-4n^{53}+4n\equiv -4n+4n\equiv 0\pmod{ 53}$ etc