Step 1: Divide the number into separate digits:
20565 => 2 0 5 6 5
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
2 to 0 = 2
0 to 5 = 5
5 to 6 = 1
6 to 5 = 1
5 to 2 = 3
Step 3: Combine the filters to a string:
2 5 1 1 3 = 25113