Step 1: Divide the number into separate digits:
2479 => 2 4 7 9
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
2 to 4 = 2
4 to 7 = 3
7 to 9 = 2
9 to 2 = 7
Step 3: Combine the filters to a string:
2 3 2 7 = 2327