Step 1: Divide the number into separate digits:
7523 => 7 5 2 3
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
7 to 5 = 2
5 to 2 = 3
2 to 3 = 1
3 to 7 = 4
Step 3: Combine the filters to a string:
2 3 1 4 = 2314