Mozart's Concerto for Horn in E flat was composed in Vienna sometime between 1784 and 1787. The Köchel number for the piece is 447, or K. 447.
Ludwig Alois Ferdinand Ritter von Köchel (1800 – 1877) was a man of many talents; he was a musicologist, writer, and composer. He is best known for cataloguing the works of Mozart and originating the 'K-numbers' by which they are known (K for Köchel). Here's a photo of him:
And here is the website of The Mozart Project, which will provide you with all you need to know about the man Professor Robert Greenberg calls "perhaps the most complete musician who ever lived."
Have a Beautiful Sunday.
