A thirteenth chord
A13 chord for piano presented by keyboard diagrams.
Explanation: The A thirteenth is a seven note chord. Due to practical circumstances, some notes (as a suggestion fifth, ninth, and eleventh) is omitted and the chord is played inverted. The chord is often abbreviated as A13.
Theory: The A thirteenth chord is constructed by adding a third to an eleventh chord.
Notes: A - C# - E - G - B - D - F#