How many 20-digit numbers can be formed from $\{1,2,3,4,5,6,7,8,9\}$ such that no 2 consecutive digit is both odd

I've noticed that the number of odd digit in the number must be less than 11. But i can't progress more than that.

I've noticed that the number of odd digit in the number must be less than 11. But i can't progress more than that.