I have the following question that I have difficulty to grasp: A string from 0,1,+,-,*,/
There are 2 rules: 1) string must start and end with a number. 2) string must not have two operators one after another.
The lecturer answer is f(n)=2f(n-1)+8f(n-2), while f(n) is the number of possible strings of length n, answering on said rules.
While 2f(n-1) is clear 8f(n-2) is not, as it creates possible duplications.