Which of the following is equal to integer?

(1) $7^{-\log _7 6}+81^{\left(1-\log _9 2\right)}=7^{-\log _7 6}+81 \cdot 81^{-\log _9 2}=\frac{1}{6}+\frac{81}{4}$ (2) \left(1-\log _6 2\right)\left(1+\log _6 2\right)+\left(\log _6 2\right)^2=1-\left(\log _6 2\right)^2+\left(\log _6 2\right)^2=1$(3)$\log _3 5+\log _3 6-\log _3 10=\log _3 3=1$(4)$\left(2^{\frac{1}{3}}+5^{\frac{1}{3}}\right)\left(2^{\frac{2}{3}}-2^{\frac{1}{3}} \cdot 5^{\frac{1}{3}}+5^{\frac{2}{3}}\right)=2+5=7