Euler is easily the most prolific mathematician of all time. The range and volume of his output is simply staggering. He published over 850 papers, almost all of substantial length, and more than 25 books and treatises. In 1907 the Swiss Academy of Sciences established the Euler Commission with the charge of publishing the complete body of work consisting of all of his papers, manuscripts, and correspondence. This project, known as Opera Omnia, began in 1911 and is still ongoing. His scientific publications, not counting his correspondence, run to over 70 volumes, each between approximately 300 and 600 pages. Thousands of pages of handwritten manuscripts are still not in print. Euler was in constant communication with all the great scientists of his day, and his correspondence covers several thousand pages. Euler's powers of memory and concentration were legendary. He could recite the entire Aeneid word-for-word. He was not troubled by interruptions or distractions; in fact, he did much of his work with his young children playing at his feet. He was able to do prodigious calculations in his head, a necessity after he went blind. The contemporary French mathematician Condorcet tells the story of two of Euler's students who had independently summed seventeen terms of a complicated infinite series, only to disagree in the fiftieth decimal place; Euler settled the dispute by recomputing the sum in his head. Further reading: http://www.ams.org/bookstore/pspdf/euler-prev.pdf Links: The Euler Archive - Dartmouth College Digitized publications at the Berlin-Brandenburgische Akademie der Wissenschaften Digitized publications at the University of Strasbourg Some manuscripts at the Berlin-Brandenburgische Akademie der Wissenschaften Some further reading on Leonhard Euler