As you probably know, until Christmas I have decided to substitute my monthly favorites with a post about 3 great mathematicians born in the previous month. So, because today is the 1st of October, I have decided to write a little about 3 great mathematicians born in September. Enjoy!

**Adrien-Marie Legendre**, was born on 18th September 1752, worked mostly on elliptic integrals provided basic analytical tools for mathematical physics. He is well-known for concepts such as Legendre polynomials and Legendre transformation. The Legendre transformation is commonly used in classical mechanics and in thermodynamics. Associated Legendre polynomials are the most general solution to Legendre’s Equation. This is an ordinary differential equation frequently found in physics.

Legendre is also known for his simple proof that π is irrational as well as the first proof that π^{2} is irrational. Very interesting is the fact that the only existing portrait of this mathematician is a 20 watercolor caricature made by the French artist Julien Leopold Boilly.

**Dimitrie Pompeiu**, born on 22nd September 1873, was a Romanian mathematician who worked in mathematical analysis, complex function theory and rational mechanics. I had to put him for this month because he was born in a village close to my hometown and he has done his primary and secondary school in the small town I was born in Romania. He did his PhD under the famous French mathematician Henri Poincaré in 1905.

**Harald Cramér**, born on 25th September 1873, was a Swedish mathematician, actuary and statistician, specializing in mathematical statistics and probabilistic number theory. He was sometimes referred as *“one of the giants of statistical theory”*. When he first got interested in probability, this was not an accepted branch of mathematics. At that time he realized that there should be a radical change in this field, so he became focused on the rigorous mathematical formulation of probability. He stated that *“The probability concept should be introduced by a purely mathematical definition, from which its fundamental properties and the classical theorems are deduced by purely mathematical operations.”*

Special mention for this month are Marin Mersenne and Bertrand Riemann. I did not want to write about them in this post because I have done that in the past: Marin Mersenne and Bertrand Riemann.

Hope you enjoyed this post and that you are excited for the future ones. Have a great week. You can find me on Facebook, Tumblr, Google+, Twitter and Instagram. I will try to post there as often as possible.

*Don’t forget that maths is everywhere! Enjoy! *