Rabbit sequence 1,2,3,5,8 Each number is the sum of its first two terms. What is the number 1991?
This is a problem of finding the general term formula, n (1) = 1, n (2) = 2... N (k) = n (k-1) + n (K-2) k > = 3. General term formula: n (k) = (1 / √ 5) * {[(1 + √ 5) / 2] ^ k - [(1 - √ 5) / 2] ^ k}. The amount of calculation is quite large, so it is recommended to use a calculator