piano chord
E6
E1G♯3B5C♯6
A major triad with a sixth added. The same four notes as a minor seventh chord a third below.
What is true of it
E6 is E, G♯, B and C♯ — 1, 3, 5 and 6 counted from E.
These are also the notes of C♯m7/E and D♭m7/E. Which name is right depends on what is underneath and what came before — the notes alone do not decide.
On an instrument that cannot reach all 4, the 5 goes first, in that order.