Step 1: Divide the number into separate digits:
2619 => 2 6 1 9
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
2 to 6 = 4
6 to 1 = 5
1 to 9 = 8
9 to 2 = 7
Step 3: Combine the filters to a string:
4 5 8 7 = 4587