A 5/C#
The A 5 chord consists of the A (Perfect unison) and E (Perfect fifth) notes, with C# as the bass note.

How to play the A 5/C# chord
- Play C# as the lowest bass note in the left hand
- Find A (Root) on the piano keyboard
- Add E (Perfect fifth) — 7 semitones above A
- Press all 3 notes simultaneously to sound the A 5/C# chord