Step 1: Divide the number into separate digits:
2369 => 2 3 6 9
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
2 to 3 = 1
3 to 6 = 3
6 to 9 = 3
9 to 2 = 7
Step 3: Combine the filters to a string:
1 3 3 7 = 1337