In terms of chords and melody, 3s and 7s is significantly more complex than the typical song, having above average scores in Chord Complexity, Melodic Complexity, Chord-Melody Tension, Chord Progression Novelty and Chord-Bass Melody.
3s and 7s has sections analyzed in the following keys: B♭ Dorian, G♯ Minor, and F Minor. Click on the linked cheat sheets for popular chords, chord progressions, downloadable midi files and more!