I would guess it would be 46,656.
There are 10 numbers and 26 letters or a possibility of 36 different characters in each position.
Therefore 36 x 36 x 36 is 46,656.
At least a full day of branding, right.
Thiis would, of course assume the characters are right side up
and in one place on the cattle.
If you allow the characters to be oriented in four ways, you would
get 144 x 144 x 144 or 2,985,984. If there are 10 places to brand a critter, you would get 29,859,840.
If you really want to get precise, adjust the numbers downward for zeros and o's which look the same any which way.
I'm not going to figure that one out.
cp