The pattern for flat major scales (and F Maj) are based on BEAD-GC so starting with Fmaj we get:
F maj = Bb <== also notice that Bb will be the next scale
Bb maj = Bb, Eb
Eb maj = Bb, Eb, Ab
Ab maj = Bb, Eb, Ab, Db
Db maj = Bb, Eb, Ab, Db, Gb
Cb maj = Bb, Eb, Ab, Db, Gb, Fb <== OK This one ends with Fb
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