Leonhard Euler

Leonhard Euler was born on 15 April 1707 in Basel, Switzerland, and died on 18 September 1783 in Saint Petersburg, Russia. He worked at the Saint Petersburg Academy from 1727 to 1741, the Berlin Academy from 1741 to 1766, then returned to Saint Petersburg for the rest of his life. He was the first to treat sine, cosine and the other trigonometric ratios as functions rather than as chords, and he introduced notation still in use today, including f(x) for a function, e for the base of the natural logarithm, i for the imaginary unit and the summation sign. His 1748 Introductio in analysin infinitorum established analysis as the study of functions, and his Institutiones calculi differentialis and Institutiones calculi integralis remained standard calculus texts for generations. He solved the Basel problem, proving that the sum of the reciprocals of the perfect squares equals pi squared over six. He continued to publish prolifically after losing his eyesight, producing roughly half his life's output afterward through memory and the help of assistants, and is generally reckoned the most prolific mathematician in history.