Step 1: Divide the number into separate digits:
5212 => 5 2 1 2
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
5 to 2 = 3
2 to 1 = 1
1 to 2 = 1
2 to 5 = 3
Step 3: Combine the filters to a string:
3 1 1 3 = 3113