A 6/9 chord
A6/9 chord for piano with keyboard diagram.
Explanation: The A sixth/ninth is a five-note chord. Due to practical circumstances, however, the fifth (E) is often omitted and/or the chord is played inverted. The chord is abbreviated A6/9. It can also be written A6add9 or Amaj6add9.
Theory: The A6/9 chord is constructed with a root, a major third, a perfect fifth, a major sixth and a major ninth. That gives the chord formula 1 - 3 - 5 - 6 - 9.
Notes: A - C# - E - F# - B