[tex]2\cdot(n+1) | 18\Rightarrow 2\cdot(n+1)\in D_{18} =\{1,2,3,6,9,18\}.\\2\cdot(n+1)=1~! \\
2\cdot(n+1)=2\Rightarrow \boxed{n=0} \\
2\cdot(n+1)=3~! \\
2\cdot(n+1)=6\Rightarrow \boxed{n=2} \\
2\cdot(n+1)=9~!~ \\
2\cdot(n+1)=18\Rightarrow \boxed{n=8}\\ Obs.:~!~inseamna~nu~convine.[/tex]
