C maj13/C#
The C maj13 chord consists of the C (Perfect unison), E (Major third), G (Perfect fifth), B (Major seventh), D (Major ninth) and A (Major thirteenth) notes, with C# as the bass note.

How to play the C maj13/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 B (Major seventh) — 11 semitones above C
- Add D (Major ninth) — 14 semitones above C
- Add A (Major thirteenth) — 21 semitones above C
- Press all 7 notes simultaneously to sound the C maj13/C# chord