Step 1: Divide the number into separate digits:
6419 => 6 4 1 9
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
6 to 4 = 2
4 to 1 = 3
1 to 9 = 8
9 to 6 = 3
Step 3: Combine the filters to a string:
2 3 8 3 = 2383