A m13/B
The A m13 chord consists of the A (Perfect unison), C (Minor third), E (Perfect fifth), G (Minor seventh), B (Major ninth) and F# (Major thirteenth) notes, with B as the bass note.

How to play the A m13/B chord
- Play B as the lowest bass note in the left hand
- Find A (Root) on the piano keyboard
- Add C (Minor third) — 3 semitones above A
- Add E (Perfect fifth) — 7 semitones above A
- Add G (Minor seventh) — 10 semitones above A
- Add B (Major ninth) — 14 semitones above A
- Add F# (Major thirteenth) — 21 semitones above A
- Press all 7 notes simultaneously to sound the A m13/B chord