Leonhard Euler (1707-1783) was surely one of the most prolific of great mathematicians. Among his contributions, we need to mention two, each of which comes down to us as a single letter: the letter e and the letter i . If we were literally to "pay"tribute, we might do so in increments of $2.72, rounding up a bit the value of irrational e. We'll get to that. First: biography. Euler was born in Basel, Switzerland, so his life and work might fittingly be considered a riposte to the old anti-Swiss jibe (originally from The Third Man ) that Switzerland has produced nothing for all its years of peace and democracy, nothing more than the humble cuckoo clock. Since Euler’s day and because of his work, i has stood for the simplest of the numbers that Descartes had called “imaginary.” This i refers to the square root of -1. We don’t need to bother ourselves further with the question “ what is the square root of -1?” It is i , by stipulation. Also since Eul...