piano chord
F♯11
F♯1A♯3C♯5E♭7G♯9B11
Six notes in theory; in practice the third is usually dropped, because the eleventh sits a half step above it.
Written the other way round it is G♭11 — the same twelve keys on a piano, a different piece of notation.
What is true of it
F♯11 is F♯, A♯, C♯, E, G♯ and B — 1, 3, 5, b7, 9 and 11 counted from F♯.
On an instrument that cannot reach all 6, the 3, 5 and 1 go first, in that order.