His achievements ranged across almost every field of mathematics.

He introduced the idea of function and much of modern notation, including that for trigonometric functions, the letter e for the base of natural logarithms, sigma for summations, and the letter i to represent the square root of negative one.

Euler developed the concept of power series, worked out that the sum of the reciprocal squares was pi squared on six, suggested the law of quadratic reciprocity, created graph theory to solve the Konigsberg bridge problem, defined the Gamma function, did important work in differential equations and the calculus of variations ... the list goes on.

His most well known result is probably

^{th}, Lenny !!