Step 1: Divide the number into separate digits:
41987 => 4 1 9 8 7
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
4 to 1 = 3
1 to 9 = 8
9 to 8 = 1
8 to 7 = 1
7 to 4 = 3
Step 3: Combine the filters to a string:
3 8 1 1 3 = 38113