Evolutio producti infiniti (1-x)(1-xx)(1-x^3)(1-x^4)(1-x^5) etc. in   seriem simplicem
  This paper does exactly what the title says it does. It expands the given series to arrive at the familiar "pentagonal number" expansion, also known as the pentagonal number theorem, and recalls its application to partition numbers. The paper is translated from Euler's Latin original into German. 
Leonhard Euler, Artur Diener, Alexander Aycock
math.HO