You have to fill numbers in place of question marks. The numbers that you can use are 1, 3, 5, 7, 9, 11, 13 and 15. You can repeat the numbers if you like.

Using the digits 1, 2, 3 and 4, find the number of 10-digit sequences that can be written so that the difference between any two consecutive digits is 1.

Examples of such 10-digit sequences are ********** and **********.