A b5
The A b5 chord consists of the A (Perfect unison), C# (Major third) and D# (Diminished fifth) notes.

How to play the A b5 chord
- Find A (Root) on the piano keyboard
- Add C# (Major third) — 4 semitones above A
- Add D# (Diminished fifth) — 6 semitones above A
- Press all 3 notes simultaneously to sound the A b5 chord