In music, Op. 31 stands for Opus number 31. Compositions that are assigned this number include: * Alkan – Preludes, Op. 31 * Barber – Summer Music * Beethoven – Piano Sonata No. 16 * Beethoven – Piano Sonata No. 17 * Beethoven – Piano Sonata No. 18 * Britten – Serenade for Tenor, Horn and Strings * Chopin – Scherzo No. 2 * Elgar – A Song of Flight * Elgar – After * Enescu – Vox Maris * Farrenc – Piano Quintet No. 2 * Górecki – Symphony No. 2 * Gottschalk – Souvenir de Porto Rico * Prokofiev – Tales of an Old Grandmother * Rachmaninoff – Liturgy of St. John Chrysostom * Saint-Saëns – Le rouet d'Omphale * Schillings – Mona Lisa * Schoenberg – Variations for Orchestra * Schumann – 3 Gesänge * Tchaikovsky – Marche slave * Vierne – Vingt-quatre pièces en style libre This di