Bb Major 9#11, 4th inversion (B# in the bass)
Also written as Bbmaj9#11/B#.
Notes, from the bass up
B# (bass)EA#DE#A
The same notes as Bb Major 9#11 (B#, E, A#, D, E# and A), rearranged so B# is the lowest note. Use it to move between chords with smaller jumps across the keyboard.