Leonhard Euler, Swiss mathematician and physicist.

(complex analysis) The equation e^(i𝜋)=-1,!, which unifies diverse fields of mathematics.

(complex analysis) Formula which links complex exponentiation with trigonometric functions:

(differential equations) A method for numerically approximating the solution to an ordinary differential equation with a given initial value.

(topology, of a topological space) The sum of even-dimensional Betti numbers minus the sum of odd-dimensional ones.

plural of Euler characteristic

(number theory) 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.

A diagram representing some sets by contours of closed shapes, typically circles and ellipses, and indicating the relationships between the sets.

plural of Euler line

(geometry) A line that, for a given triangle, passes through several important points, including the circumcentre, orthocentre and centroid; an analogous line for certain other 2- and 3-dimensional geometric figures.