[msohcw]

In decimal, when you reach numbers after 9, there's no longer a single symbol you can use to represent the next number. Hence, you represent it as 10, which is one 10 and zero 1s. 11 is one 10 and one 1. This decimal, or base 10 system hence uses only 10 symbols, (0-9). In base 36, you can use additional other symbols, up to 36 different symbols. In this case they are 0-Z, changing to the letters of the alphabet A-Z as the remaining 26 unique symbols needed. Hence A is 11, B is 12 ... Z is 35. 36 (base 10) is then represented as 10 (base 36), one 36 and zero ones. 36^2 = 1296 (base 10) would be represented as 100 (base 36).