Step 1: Divide the number into separate digits:
25081 => 2 5 0 8 1
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 8 = 8
8 to 1 = 7
1 to 2 = 1
Step 3: Combine the filters to a string:
3 5 8 7 1 = 35871