Works for piano solo include 24 Preludes traversing all 24 major and minor keys; Prelude in C-sharp minor (Op. 3, ) from "Morceaux de fantaisie" (Op. 3); ten preludes in Op. 23; and thirteen in Op. 32. Especially difficult are the two sets of "Études-Tableaux", Op. 33 and 39, which are very demanding "study pictures". Stylistically, Op. 33 hearkens back to the preludes, while Op. 39 shows the influences of Scriabin and Prokofiev. There are also the "Six moments musicaux" (Op. 16), the "Variations on a Theme of Chopin" (Op. 22), and the "Variations on a Theme of Corelli" (Op. 42). He wrote two piano sonatas, both of which are large scale and virtuosic in their technical demands. Rachmaninoff also composed works for two pianos, four hands, including two Suites (the first subtitled "Fantasie-Tableaux"), a version of the "Symphonic Dances" (Op. 45), and an arrangement of the C-sharp minor Prelude, as well as a "Russian Rhapsody", and he arranged his First Symphony (below) for piano four hands. Both these works were published posthumously.