**Fibonacci series is given by F(n) = F(n – 2) + F(n – 1)**

∴ F(11) = F(11 – 2) + F(11 – 1) = F(9) + F(10)

Similarly F(12) ; = F(12 – 2) + F(12 – 1) = F(11) + F(10)

F(13) = F(12) + F(11)

F(14) = F(13) + F(12)……

F(20) = F(19) + F(18)

The Fibonacci series given by