Code Cracker! It's like a ROT, but - think of each number in the grid as a random letter, and all 26 are represented. For example, 4 might represent the letter G, and 5 might be the letter Q. A good old pen and paper code-cracker exercise.
Once you have cracked the code, enter the letters from these numbers into Certitude:
13-26-12 8-3-5-2-11 22-10-1-16
Good luck!
You can validate your puzzle solution with
certitude.