2.) A string that contains only 0s, 1s, and 2s is called a tenary string.

a.) Find a recurrence relation for the number of tenary strings of length n that do not contain two consecutive 1s. b.) How many tenary strings of length seven do not contain two consecutive 1s?

c.) Suppose f(n) = 4f(n/3) + 1 when n is divisible by 3, and f(1) = 2. Find f(81).