I'm far from a math whiz, so offhand I can't think of a way to get both 2 and 3 from a single formula, but I can show you how to do so in two separate ones.

To get 2 from 13/5, you can use the TRUNC() function in a calculation field (make sure to enclose the calculation whose result you want to truncate in parentheses inside the function, otherwise it won't be calculated before truncation):

TRUNC((13/5))

To get the remainder, 3, you can use the MOD (short for "modulo") operator:

13 MOD 5

You can see the results for yourself in this sample macro, which uses the %Calculate% token to create a calculation field within a plain text field and enable these functions: