The story
Named after Leonhard Euler (1707–1783), Swiss mathematician and physicist, who devised the criterion in 1748.
Etymology from Wiktionary, CC BY-SA 4.0.
Euler's criterion
Today it means: A theorem which states that, given a positive integer a which is coprime to an odd prime number p, a is a quadratic residue of p if and only if a^((p-1)/2) is congruent to 1 modulo p. Full definition →