Hey guys,

My program basically accepts an index(less than 46) and determine whether it's fibonacci number is prime or not . i am basically done with my program which determine whether the but its not returning the right output. I tried debugging to see if the fibonacci number is correct and it is. i really dont know whats wrong.

Here are indexes known to be prime: 3, 4, 5, 7, 11, 13, 17, 23, 29, 43

some sites suggests that 19, 31, 37, 41 are primes as well but that I do not know.

My program tells me these indexes are prime: 3, 4, 5, 7, 11, 13, 17, 19, 22, 23, 26, 29, 31, 34, 37, 38, 41, 43, 46

I also tried changing the divisor instead of from (2 - 20) to (2 - input), but then it returns the answer VERY SLOW for very large indexes. Please find the problem. Thanks in advance

Heres the code

Code:#include <stdio.h> int fibo(int n); int fibo_prime(int n); int prime(int n); int main() { int n; int result; printf("Enter a positive integer as Fibonacci index(less than 46): "); scanf("%d", &n); result = fibo_prime(n); if (result == 0) printf("Fibonacci index %d will not result in a Fibonacci prime!\n", n); else //if (result == 1) printf("Fibonacci index %d will result in a Fibonacci prime!\n", n); } int fibo_prime(int n) { int fibo_number; fibo_number = fibo(n); prime(fibo_number); return prime(fibo_number); } int fibo(int n) { int fib_a, fib_b, result, temp, i; temp = 0; if (n == 0) result = 0; else if (n == 1) result = 1; else { fib_a = 0; fib_b = 1; for (i = 2; i <= n; i++) { temp = fib_a; fib_a = fib_b; fib_b = temp + fib_a; result = fib_b; } } return result; } int prime(int n) { int divisor; int prime = 1; //Assume the number is prime if (n == 1) return 0; else { for (divisor = 2; divisor <= 20; divisor++) { //for divsior between 2 - input if (((n%divisor) == 0) &&(n != divisor))// TEST number if its prime or not prime = 0; } if (prime) return 1; else return 0; } }