Bb Augmented Major 7th, 3rd inversion (A in the bass)
Also written as Bbaug(maj7)/A.
Notes, from the bass up
A (bass)A#DF#
The same notes as Bb Augmented Major 7th (A, A#, D and F#), rearranged so A is the lowest note. Use it to move between chords with smaller jumps across the keyboard.