Step 1: Divide the number into separate digits:
4278 => 4 2 7 8
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
4 to 2 = 2
2 to 7 = 5
7 to 8 = 1
8 to 4 = 4
Step 3: Combine the filters to a string:
2 5 1 4 = 2514