[tex]\it E(x)=2(x^2-9)-(x^2-2x+1)-16=2x^2-18-x^2+2x-1-16=\\ \\ =x^2+2x-35=x^2+2x+1-36=(x+1)^2-6^2=(x+1-6)(x+1+6)= \\ \\ =(x-5)(x+7)[/tex]
[tex]\it\ Pentru\ \ n\in\mathbb{N}\ \Rightarrow\ E(n)= (n-5)(n+7)\\ \\ E(n)\ -\ num\breve ar\ \ prim\ \ dac\breve a\ \ n-5=1 \Rightarrow\ n=6\\ \\ E(6) = 1\cdot13=13\ \ num\breve ar\ \ prim.[/tex]
