Bb 13sus4, 2nd inversion (E# in the bass)
Also written as Bb13sus4/E#.
Notes, from the bass up
E# (bass)G#B#GA#D#
The same notes as Bb 13sus4 (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.