piano chord
F6
F1A3C5D6
A major triad with a sixth added. The same four notes as a minor seventh chord a third below.
What is true of it
F6 is F, A, C and D — 1, 3, 5 and 6 counted from F.
These are also the notes of Dm7/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.