Step 1: Divide the number into separate digits:
9773 => 9 7 7 3
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
9 to 7 = 2
7 to 7 = 0
7 to 3 = 4
3 to 9 = 6
Step 3: Combine the filters to a string:
2 0 4 6 = 2046