Hexadecimal is widely recognized with A - F as the digits beyond nine. However, what about bases with even more digits, such as Base 32 and Base 64?
For Base 32, you could simply continue the alphabet, but what about Base 64, when you run out? Even if you then used lowercase letters, you'd run out of digits before you got to 64.
However, even so, this would be ignoring problems with distinguishing certain digits. For example, 1 and l. In many fonts, they are practically indistinguishable. Or, 0 O and o, while being easily distinguishable from each other in text, would likely be difficult if it was handwritten.
And that's why I'm wondering if there's some standard for Base 32 and Base 64. Presumably, if it existed, it would skip problem characters and include the necessary non-alphabetic glyphs at the end.
Oh, and even though I specifically said "standard", even just a precedent would be fine.
Base 32 is standardized, continuing where base 16 leaves off: 0,1,2,,...,9,a,b,c,...,t,u,v (upper/lower case is not distinguished). I hope I counted right ;)
Base 64 is definitely NOT standardized. You often see in base-64 encoding the use of 0-9, A-Z, a-z, and then two more characters. The choice of the additional characters, and then then choice of how to order the whole set, is not standard.
This use of base 64 is not, I think, the use you have in mind. I think you are looking for a standard way to write a base 64 number, and the various encoding methods are nothing more than a way to encrypt 8-bit data into 7-bit-compatible characters.