Step 1: Divide the number into separate digits:
1376 => 1 3 7 6
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
1 to 3 = 2
3 to 7 = 4
7 to 6 = 1
6 to 1 = 5
Step 3: Combine the filters to a string:
2 4 1 5 = 2415