C add13/C#
The C add13 chord consists of the C (Perfect unison), E (Major third), G (Perfect fifth) and A (Major thirteenth) notes, with C# as the bass note.

How to play the C add13/C# chord
- Play C# as the lowest bass note in the left hand
- Find C (Root) on the piano keyboard
- Add E (Major third) — 4 semitones above C
- Add G (Perfect fifth) — 7 semitones above C
- Add A (Major thirteenth) — 21 semitones above C
- Press all 5 notes simultaneously to sound the C add13/C# chord