Bb Power Chord (5) (Bb5)
Also written as A# Power Chord (5) (A# and Bb are the same key).
1+5
Notes in Bb Power Chord (5)
A# (root)E#
Inversions
Same notes as Bb Power Chord (5), with a different chord tone as the lowest note. Useful for smoother movement between chords instead of jumping around the keyboard.
Root position
A# in the bass
1st inversion
E# in the bass (Bb5/E#)
The notes A# and E# make up Bb Power Chord (5).
Just a root and a fifth, no third at all. That makes it neither major nor minor, which is why rock guitar and simple piano left-hand parts lean on it so much. It sounds strong and neutral, and it leaves room for a singer or another instrument to decide the mood.