Step 1: Divide the number into separate digits:
4637 => 4 6 3 7
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
4 to 6 = 2
6 to 3 = 3
3 to 7 = 4
7 to 4 = 3
Step 3: Combine the filters to a string:
2 3 4 3 = 2343