Find all positive integers $n \le 6$, such that the equation $a^n+b^n=c^n+n$ has solutions over the integers. Find all positive integers $n \le 6$, such that the equation $a^n+b^n=c^n+n$ has solutions over the integers.
My attempt:
For $n=1$, trivially there are integer solutions.
For $n=2$, we have the solutions
$$a=b=\pm 1, c=0.$$
For $n=3$, we have the solution
$$a=b=1, c = -1.$$
Anyone can complete the proof for $n=4,5,6$?

$n=4$:
fourth powers are $\equiv 0$ or $1\pmod{8}$. There is no way to have $(0\text{ or }1)+(0\text{ or }1)\equiv (0\text{ or }1)+4\pmod 8$.
$n=5$:
Fifth powers are $\equiv 0$ or $1$ or $-1\pmod{11}$. Three such numbers combined cannot produce $5$, i.e., $a^5+b^5-c^5\equiv -3,-2,-1,0,1,2,3\not\equiv 5\pmod {11}$.
$n=6$:
Sixth powers are $\equiv 0$ or $1$ or $-1\pmod{13}$. Three such numbers combined cannot produce $6$, i.e., $a^6+b^6-c^6\equiv -3,-2,-1,0,1,2,3\not\equiv 6\pmod {13}$.
