BWL:
I believe you are thinking of the duodecimal system, hardly ever heard of. Hex___ usualy refers to six, as in a hexagon. Thus, hexadecimal numeration is a base 16 counting system.
The numbers go 1...9,A,B,C,D,E,F,10..19,1A,1B,1C,1D,1E,1F,20....29, 2A, 2B, 2C, and so on.
A