A maj9/A#
The A maj9 chord consists of the A (Perfect unison), C# (Major third), E (Perfect fifth), G# (Major seventh) and B (Major ninth) notes, with A# as the bass note.

How to play the A maj9/A# chord
- Play A# as the lowest bass note in the left hand
- Find A (Root) on the piano keyboard
- Add C# (Major third) — 4 semitones above A
- Add E (Perfect fifth) — 7 semitones above A
- Add G# (Major seventh) — 11 semitones above A
- Add B (Major ninth) — 14 semitones above A
- Press all 6 notes simultaneously to sound the A maj9/A# chord