Mathematical Notation Day - April 15
On this date in 1707 the Swiss mathematician Leonhard Euler was born. (Technically he was only born Swiss; the mathematician part came later. And he was also pretty adept at physics, astronomy, engineering, logic, and geography, probably more of a polymath.) Considered one of the greatest mathematicians in history, his contributions to the field live on in much of the mathematics we do today: Assigned the Greek letter π to the number representing the ratio of a circle's circumference to its diameter (3.14...), Created the number e to represent a logarithm's natural base (2.71...), Assigned the letter i to represent the square root of -1, Introduced the notation f(x) to describe the y-axis of a function, And used Σ to represent summation.