For how many natural numbers x, is the expression: (x ² + 2x + 3) divisible by 35 ?

(In reply to Simplest solution - no moduli! by JayDeeKay)

Well, JayDeeKay, that proof is not correct.  A negative discriminant just means that f(x) = 0 has no real solution.  But f(x) can easily be non-prime.  For instance, f(4) = 27.  f(odd number) is always divisible by 2.  etc.

Edited on June 12, 2016, 8:05 am

Posted by Steve Herman on 2016-06-11 08:15:09