piano scale
A Mixolydian
A1B2C♯3D4E5F♯6G♭7
Major with a flattened seventh: the scale that fits a dominant seventh chord without altering it.
Written out
Every accidental is written in, rather than left to a key signature, so the letters can be read one at a time.
The step pattern
AWBWC♯HDWEWF♯HGWA
What is true of it
A Mixolydian is A, B, C♯, D, E, F♯ and G, and back to A.
Its steps are W – W – H – W – W – H – W, where W is a whole step and H a half.
On the same tonic, A major differs from it by exactly one note.
Chords made only of these notes
C♯dimdiminishedC♯m7♭5half-diminished seventhDmajorDmaj7major seventhEmminorEm7minor seventhF♯mminorF♯m7minor seventh
Found by testing every chord in the catalogue against these 7 sounds, not chosen.