We describe how Euler added up all positive integers into a mysterious fraction when he was 28 years old, and I try to legitimize his method “p-adically”. This is a story of Number Theory from the 17th century on. We only need some knowledge of polynomials and fractions of polynomials and very basics of differentiation. If time allows, I will enter into some results related to Ramanujan I found when I was 28 years old. For the results exposed here, a detailed proof can be found in my book: “Elementary Theory of L-functions and Eisenstein Series,” LMSST vol. 26, 1993, Cambridge U. Press.