Vigesimal

A way of writing numbers using 20 digits

Uses the normal decimal digits 0 to 9 and the letters "A" to "K" (I is not used because it looks like 1): like this:

0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F,G,H,J,K

Also called Base 20

Example: 2B in vigesimal is equal to 51 in decimal (2×20+11=51)