Step 1: Divide the number into separate digits:
25002 => 2 5 0 0 2
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
2 to 5 = 3
5 to 0 = 5
0 to 0 = 0
0 to 2 = 2
2 to 2 = 0
Step 3: Combine the filters to a string:
3 5 0 2 0 = 35020