In 1910 and 1913, Swedish Mathematician Gustav Eneström completed a comprehensive survey of Euler's works. He counted and enumerated 866 distinct works, including books, journal articles, and some letters he deemed to be especially important. Each of these was assigned a number, from E1 to E866, which is now referred to as the "Eneström number." Most historical scholars today use Eneström numbers to identify Euler's writings quickly.
The complete list was originally published as Die Schriften Eulers chronologisch nach den Jahren geordnet, in denen sie verfasst worden sind (The Writings of Euler, ordered by the year in which he wrote them) in the 1913 edition of the Jahresbericht de Deutschen Mathematiker-Vereinigung.
Eneström's index (German):
Greta Perl's 2004 translation of the Eneström Index into English is also available. These files contain a complete transcription of Eneström's original publication. These files are text-searchable, and Eneström's original comments and notes in German have all been translated into English.
Eneström's index (English):