Step 1: Divide the number into separate digits:
1950 => 1 9 5 0
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
1 to 9 = 8
9 to 5 = 4
5 to 0 = 5
0 to 1 = 1
Step 3: Combine the filters to a string:
8 4 5 1 = 8451