Step 1: Divide the number into separate digits:
8702 => 8 7 0 2
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
8 to 7 = 1
7 to 0 = 7
0 to 2 = 2
2 to 8 = 6
Step 3: Combine the filters to a string:
1 7 2 6 = 1726