For those mathematically inclined, I highly recommend "Introduction to the Analysis of the Infinite": https://www.springer.com/us/book/9780387968247 https://www

For those mathematically inclined, I highly recommend "Introduction to the Analysis of the Infinite": https://www.springer.com/us/book/9780387968247 https://www.springer.com/us/book/9780387968247 It's fascinating to see how Euler thought about things like infinite series, derivatives, etc. before they were formalized hundreds of years later. You'll find him make "mistakes" (i.e.,assumptions which are not true) but he always gets the right answer. Look for, in particular, his proof that \sum \frac{1}{n^2} = \frac{\pi^2}{6}.