piano chord
A♯dim7
A♯1C♯♭3E♭5G♭♭7
Three minor thirds stacked. The seventh is doubly diminished, which is why it is written with a double flat.
Written the other way round it is B♭dim7 — the same twelve keys on a piano, a different piece of notation.
What is true of it
A♯dim7 is A♯, C♯, E and G — 1, b3, b5 and bb7 counted from A♯.