Question

Find the sum of all primes p, such that p divides up, where up is the p- th Fibonacci number.

please tell me the answer it's urgent about this..///

Answer 1

If we use binets formula for the fibonacci numbers we can trivially see that Fp=5^(p-1)/2 mod p implying that the only prime p such that p divides Fp is 5 divides F5=5.