Step 1: Divide the number into separate digits:
7539 => 7 5 3 9
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
7 to 5 = 2
5 to 3 = 2
3 to 9 = 6
9 to 7 = 2
Step 3: Combine the filters to a string:
2 2 6 2 = 2262