18.24Blues scale

Start with minor pentatonic:

1 ♭3 4 5 ♭7

Add:

♭5

So the blues scale is:

1 ♭3 4 ♭5 5 ♭7

For C:

C E♭ F G♭ G B♭

For A:

A C D E♭ E G

That added ♭5 is often called the blue note.