Explanation:
that is not mathematics, and I am not sure, if you listed everything, but the result to such a loop is
25811
because it first prints the Imuran content of c (2).
then it increases the content of c by 3. c is now 5
then it checks that 5 is still smaller than 12 (yes it is), and it prints 5.
then it prints 8. then 11. and then c becomes 14 and is therefore larger than 12. and the loop ends.
I don't know what your particular print command does, but I assume it is just a basic "bring the parameter to output". in that case it will write all numbers right after the previous number.
hence : 25811