26675

It's always even.

X² - X = even.
if X is odd.
X² is odd.
so X² - X = even.
if X is even.
X² is even.
so X² - X = even.

Side proof : how even - even = even and odd - odd = even:

If n and e is an arbitrary whole number, then even = 2n, so even - even =
2n - 2e = 2(n - e). Thereby, even - even = even.

So odd = 2n + 1. So odd - odd = 2n + 1 - (2e + 1) = 2n - 2e + 1 - 1 = 2(n - e).
Thereby, odd minus odd = even.