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

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