C 13#11, 3rd inversion (Bb in the bass)
Also written as C13#11/Bb.
Notes, from the bass up
Bb (bass)DF#ACEG
The same notes as C 13#11 (Bb, D, F#, A, C, E and G), rearranged so Bb is the lowest note. Use it to move between chords with smaller jumps across the keyboard.