Arata ca F este numar natural.

[tex]\displaystyle\\F = \frac{3^4-1}{2^{15}:2^{12}}\\ \\F = \frac{81-1}{2^{15-12}}\\ \\F = \frac{80}{2^3} \\ \\F = \frac{80}{8} \\ \\F = 10 \in \mathbb{N}[/tex]