F Viennese trichord/A#
The F Viennese trichord chord consists of the F (Perfect unison), F# (Minor second) and B (Diminished fifth) notes, with A# as the bass note.

How to play the F Viennese trichord/A# chord
- Play A# as the lowest bass note in the left hand
- Find F (Root) on the piano keyboard
- Add F# (Minor second) — 1 semitone above F
- Add B (Diminished fifth) — 6 semitones above F
- Press all 4 notes simultaneously to sound the F Viennese trichord/A# chord