Solve the below:
Q: Let a(subn) equal the number of ternary strings of length n made up of 0s,1s,and 2s, such that the substrings 00,01,10, and 11 never occur.
Prove that a(subn)= a(subn-1) + 2a(subn-2), (n>=2) with a(sub 0)=1 and a(sub1)=3 Then find a formula for a(sub n)