Step 1: Divide the number into separate digits:
53491 => 5 3 4 9 1
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
5 to 3 = 2
3 to 4 = 1
4 to 9 = 5
9 to 1 = 8
1 to 5 = 4
Step 3: Combine the filters to a string:
2 1 5 8 4 = 21584