Aternary string is a sequence of 0's, 1's and 2's. just like a bit string, but with three symbols. let's call a ternary string good provided it never contains a 2 followed immediately by a 0. let g n gn be the number of good strings of length n . n. for example, g 1 = 3 , g1=3, and g 2 = 8 g2=8 (since of the 9 ternary strings of length 2, only one is not good).