Showing that $a = 2^{1264504 }- 1$ is not prime

Question

Is there a simple way to show this? Quite new to these kind of proofs. I tried writing down the powers:
$2^0 - 1 = -1 \\ 2^1 - 1 = 1 \\ 2^2 - 1 = 3 \\ 2^3 - 1 = 7 \\ 2^4 - 1 = 15 \\ 2^5 - 1 = 31$
...
I'm not sure what to do from here...

Answer 1

HINT

Notice that you are raising 2 to an even power, and remember that $$ a^2-1 = (a+1)(a-1) $$

Answer 2

It is divisible by $3$ since $2^2\equiv 1\mod3$, so $$2^{1264504}-1=(2^2)^{632252}-1\equiv 1^{632252}-1=0\mod3.$$