Hi Folks,
Need some help with math here.

I have to find out the number of combinations possible for a 6 character string.

The rules are as follows:

I can use all the 26 letters and digits from (0 - 9)
None of the strings should start with a letter.

eg:- A12345 is invalid. 12A345 is valid

None of the strings should end with a letter.

12345A is invalid. 12AB34 is valid.

None of the strings should start with a zero.
012A34 is invalid. 12A340 is valid.

Each output string should contain atleast one alphabet, but no more than 5 alphabets.

How do I start to figure this?

Help Folks,
abhijit