While studying Fibonacci numbers, I came up with this problem. Of course $F_n = F_{n-1}+F_{n-2}$. I'm sort of stuck with first realizing how to show a number actually isn't a Fibonacci number. I thought that I could somehow rewrite the sum $$F_n+\cdots+F_{n+7}$$ into some sort of rearrangement of $F_n$'s and $F_{n+1}$'s. Could anyone help me show that the sum of 8 consecutive Fibonacci numbers is not a Fibonacci number?
Thanks