piano chord
B♭13
B♭1D3F5A♭♭7C9G13
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 A♯13 — the same twelve keys on a piano, a different piece of notation.
What is true of it
B♭13 is B♭, D, F, A♭, C and G — 1, 3, 5, b7, 9 and 13 counted from B♭.
On an instrument that cannot reach all 6, the 5, 9 and 1 go first, in that order.