Abstract: "Simone Weil is one of the most prominent 20th century French philosophers. She is the sister of Andr{é} Weil, the renowned mathematician, the father of modern algebraic geometry and the initiator of the Bourbaki group. Simone and Andr{é} Weil shared a love for literature, mathematics, science and philosophy. My aim in this article is to convey, based on their writings and their correspondence, the idea that Pythagoreanism was a central element of their thought. I will put this into context, talking first about the life and work of each of them, showing how much they were linked by essential common ideas, even though their life paths were very different, and how, ultimately, Pythagorean mathematics and philosophy became naturally part of their respective intellectual worlds. The article is the written version of a lecture I gave in October 2025, at the conference ``The Life and Contribution of Pythagoras to Mathematics, Sciences, and Philosophy'' that took place on October 3-4, 2025 at the Cyprus University of Technology in Limassol"