Beethoven's early sonatas were highly influenced by those of Haydn and Mozart. The first three sonatas, written in 1782-3 are usually not acknowledged as part of the complete set of piano sonatas, due to the fact that he was 13 when they were published.[4] His Piano Sonatas No. 1, 2, 3, 4, 7, 11, 12, 13, and 15 are four movements long, which was rather uncommon in his time.