There is a good reason for the Bunyakovsky conjecture to be open, it is very hard to find a counterexample and even for polynomials that seem to be one, there are cases where you have to wait for very high $x$ until you encounter a prime. See for exampe the one given at wolfram: $x^{12}+488669$ it produces the first prime for $x=616980$, the first prime is therefore bigger than $10^{69}$.
Using GMP you can try if there might be a possible counterexample in your sequence:
#include #include using namespace std; int Rabin_Miller(mpz_class n) { /* given an integer n >= 3 returns 0 composite, 1 probably prime */ return mpz_probab_prime_p(n.get_mpz_t(), 10); } #define MAX_A 1000000 #define MAX_X 1000 int main() { mpz_class a; for(a = 4; a < MAX_A; ++a) { for(unsigned int x = 1; x <= MAX_X; ++x) { if(Rabin_Miller(x*x+a*x+a) > 0) x = MAX_X+1; if(x == MAX_X) cout << "For a = " << a << " the first " << MAX_X << " values are composite!" << endl; } } }
I used it to see (takes over 10 minutes to compute) that if there is a counterexample then $a>10.000.000$ (the above source is for 1 million, also note gmp uses the rabin miller test which only tells you if a number is probably prime but for prime numbers that are small like the ones in this program, it works correct [I think no example where it fails is known]).