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