piano chord
F♯13
F♯1A♯3C♯5E♭7G♯9D♯13
Seven notes in theory and four or five in anyone’s hands: root, third, seventh and thirteenth carry it.
Written the other way round it is G♭13 — the same twelve keys on a piano, a different piece of notation.
What is true of it
F♯13 is F♯, A♯, C♯, E, G♯ and D♯ — 1, 3, 5, b7, 9 and 13 counted from F♯.
On an instrument that cannot reach all 6, the 5, 9 and 1 go first, in that order.