I didn't know about:

    {A..C}{0..3}

"This sequence creates every combination of A to C and 0 to 3—i.e. A0, A1, A2, A3, B0, B1, etc."

And:

    echo {a..z..2}
    a c e g i k m o q s u w y

"The ..2 bit tells the expansion to only output every second letter."