Fig. 1 · A# to F##

interval

A♯ major sixth

A♯lowerF𝄪upperM69 half steps

Nine half steps. The minor third turned upside down.

On the keyboard

F𝄪A#
Fig. 2

What is true of it

A♯ up a major sixth is F𝄪: 9 half steps, and 6 letters counting both ends.

Turn it upside down — put the A♯ on top — and it becomes a minor third. The two numbers always add to nine, and the two sizes to twelve.

It is a imperfect consonance.

Every interval on A♯

A♯ → Bminor second · dissonanceA♯ → B♯major second · dissonanceA♯ → C♯minor third · imperfect consonanceA♯ → C𝄪major third · imperfect consonanceA♯ → D♯perfect fourth · perfect consonanceA♯ → D𝄪augmented fourth · dissonanceA♯ → Ediminished fifth · dissonanceA♯ → E♯perfect fifth · perfect consonanceA♯ → F♯minor sixth · imperfect consonanceA♯ → G♯minor seventh · dissonanceA♯ → G𝄪major seventh · dissonance

C M6C♯ M6D♭ M6D M6D♯ M6E♭ M6E M6F M6all 204