Step 1: Divide the number into separate digits:
42987 => 4 2 9 8 7
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
4 to 2 = 2
2 to 9 = 7
9 to 8 = 1
8 to 7 = 1
7 to 4 = 3
Step 3: Combine the filters to a string:
2 7 1 1 3 = 27113