piano chord
A♯maj9
A♯1C𝄪3E♯5G𝄪7B♯9
A major seventh with a ninth on top.
Written the other way round it is B♭maj9 — the same twelve keys on a piano, a different piece of notation.
What is true of it
A♯maj9 is A♯, C𝄪, E♯, G𝄪 and B♯ — 1, 3, 5, 7 and 9 counted from A♯.
C𝄪 and G𝄪 are double sharps, and they have to be: every letter from A♯ upwards is used once, so the 3 cannot be written any other way.
On an instrument that cannot reach all 5, the 5 and 1 go first, in that order.