Yeah, the Pythagorean Theorem is hard fuck*ng core.
It's not my favourite equation, though.
That would be:
Xn + yn = zn has no non-zero integer solutions for x, y and z when n > 2.
ROCK ON, FERMAT.
You can see how Fermat's last theorem is directly related to Pythagoras' theorem.
Read more about Andrew Wiles' <Proof> of Jough's nomination for Equation of the Era
Here and see how this equation eluded mathematicians for a really, really long time.