Step 1: Divide the number into separate digits:
6237 => 6 2 3 7
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
6 to 2 = 4
2 to 3 = 1
3 to 7 = 4
7 to 6 = 1
Step 3: Combine the filters to a string:
4 1 4 1 = 4141