Introduction
Infinite series, that is an infinite sum of the form
occupy a central and important place in modern mathematics. Much of this topic was developed during the seventeenth century. Leonhard Euler continued this study and in the process
solved many important problems.
The purposes of this lecture are (i) to collect together some interesting and intriguing results
connected with in¯nite series, (ii) to present these results in a simple way, perhaps sacri¯cing
absolute standards of mathematical rigour to show sensitivity to the historical origin of the
results, (iii) to give examples of genuinely interesting extended arguments and, (iv) to demon-
strate the possibilities of elementary arguments { that is to say arguments not involving any
advanced theory.
In particular we will review Euler's argument involving one of the most surprising series. I
am not claiming this is a proof by modern standards { Euler certainly took many audacious
steps. However his boldness is refreshing, although the reader may feel uneasy during the
course of the supposed proofs. Identifying these false steps and ¯lling in the gaps is a task I
believe well worth the e®ort. Perhaps I might claim that this is an argument a good A-level
student could follow.
2 Before