Step 1: Divide the number into separate digits:
02715 => 0 2 7 1 5
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
0 to 2 = 2
2 to 7 = 5
7 to 1 = 6
1 to 5 = 4
5 to 0 = 5
Step 3: Combine the filters to a string:
2 5 6 4 5 = 25645