Step 1: Divide the number into separate digits:
9740 => 9 7 4 0
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
9 to 7 = 2
7 to 4 = 3
4 to 0 = 4
0 to 9 = 9
Step 3: Combine the filters to a string:
2 3 4 9 = 2349