A major 13th chord
Amaj13 chord for piano with keyboard diagram.
Explanation: The A major thirteenth is a six-note chord (the 11th, D in the case of Amaj13, is normally excluded). For practical reasons the chord is normally played with omitted notes and/or inverted. It is often abbreviated as Amaj13 (not to be confused with A13).
Omissions: Amaj13(no5): A - C# - G# - B - F#, Amaj13(no9): A - C# - E - G# - F#.
Theory: The A major thirteenth chord is constructed by extending the major eleventh chord with a major thirteenth note.
Notes: A - C# - E - G# - B - F#