The composer Sergei Rachmaninoff produced a number of solo piano pieces that were either lost, unpublished, or not assigned an opus number. While often disregarded in the concert repertoire, they are nevertheless part of his oeuvre. He composed sixteen such pieces, and all others are lost. Ten of these pieces were composed before he completed his Piano Concerto No. 1, his first opus, and the rest interspersed throughout his later life. In these casual works, he draws upon the influence of other composers, including Frédéric Chopin and Pyotr Tchaikovsky. The more substantial works, the Three Nocturnes and Four Pieces, are sets of well-thought out pieces that are his first attempts at cohesive structure among multiple pieces. Oriental Sketch and Prelude in D minor, two pieces he composed very late in his life, are short works that exemplify his style as a mature composer. Whether completed as a child or adult, these pieces cover a wide spectrum of forms while maintaining his characteristic Russian style.