Step 1: Divide the number into separate digits:
6461 => 6 4 6 1
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
6 to 4 = 2
4 to 6 = 2
6 to 1 = 5
1 to 6 = 5
Step 3: Combine the filters to a string:
2 2 5 5 = 2255