If x is a positive integer and f(x) = x*(x+1)^3  1 is a prime p, then sigma(p) = p+1 = x*(x+1)^3.
Everyone knows there are infinitely many x for which f(x) is prime (Bunyakovsky and BatemanHorn conjectures), but nobody knows how to prove it.
The smallest such x is 1.
