Incrementing alpha characters. Base36

Afternoon all,

Came upon a problem needed at work where i'm having some trouble programming the solution. They are looking for a simple program which takes entry of a 6 digit "number" as a START number, then another 6 digit "number" as an ending number. The program needs to generate the numbers inbetween (inclusive of the start and end).

For example:

Start 100000

End 100011

would generate:

100000

100001

100002

100003

100004

100005

100006

100007

100008

100009

100010

100011

I wrote this without any problems several months ago. The trouble now is, they specifications have changed. The last 4 digits of the 6 digit number now will no longer be base10, but base 36. So for example:

Start: 100000

End: 100011

Needs to generate:

would generate:

100000

100001

100002

100003

100004

100005

100006

100007

100008

100009

10000A

10000B

10000C

...

10000X

10000Z

100010

100011

I'm having trouble on how to accomplish this. My first though was to handle each of the last 4 characters individually, increment the ones digit from 0-Z, then increment the tens digit and so on, however, that seems very not efficient.

So, any advice would be terrific. Thanks in advance.