A little bit of math work will make your program much simpler. Grade 60-100 for GPA 0 - 4, this is a straight line! The equation for this straight line is GPA = 0.1*(grade-60). Don't forget to take care of negative GPAs.
The integer sequence is not shown (at least for me), but you can get the idea from the test cases. Here is the sequence, if you are looking for it: 1, 1, 1, 2, 5, 21, 233, 10946, 5702887...
These numbers are from the original Fibonacci sequence. To crack it, you'll need to find the relationship between these numbers and their indices.