piano chord
F♯6
F♯1A♯3C♯5D♯6
A major triad with a sixth added. The same four notes as a minor seventh chord a third below.
Written the other way round it is G♭6 — the same twelve keys on a piano, a different piece of notation.
What is true of it
F♯6 is F♯, A♯, C♯ and D♯ — 1, 3, 5 and 6 counted from F♯.
These are also the notes of D♯m7/F♯ and E♭m7/F♯. 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.