Note that there are only eleven z's in the string in red above; not twelve.

I thought most systems these days came with bc and/or dc.

Code:

$ echo '62 12^p' | dc
3226266762397899821056
$ echo '62^12' | bc
3226266762397899821056
$ 

Unfortunately, standard versions of bc are only required to handle input bases between 2 and 16 (inclusive) and dc isn't in the standards (but frequently has the same limits) so calculation in base 36 or base 62 aren't handled directly by these utilities. (On many systems, bc is implemented as a front-end to dc.) But from the above bc and dc output, I can say that 1000000000000 (base 62) (that is a digit 1 followed by twelve digit 0s) is 3226266762397899821056 (base 10).