Mathematically, how many permutations and combinations of numbers with a length of 7 and uppercase and lowercase letters can there be?

There are two understandings of the meaning of this question.

The first kind. Construct an arrangement with numbers and letters, that is, consider the order.

The options for each number are, 10 numbers, 26 uppercase letters and 26 lowercase letters. What is * * *? 10+26+26=62 species.

Therefore, the total number of programs is: 62 7? =? 352 16 14606208? Kindness About 3.5 trillion.

The second kind. Regardless of the order, use different units to form a combination.

This requires programming enumeration, and there is no direct formula calculation.

What is the result of program calculation? 969443904 combination scheme. About 960 million.

Attachment: calculation results and fortran code