Bb 13b9, 2nd inversion (E# in the bass)
Also written as Bb13b9/E#.
Notes, from the bass up
E# (bass)G#BGA#D
The same notes as Bb 13b9 (E#, G#, B, G, A# and D), rearranged so E# is the lowest note. Use it to move between chords with smaller jumps across the keyboard.