\(B=3+\left(3^2+3^3+3^4\right)=\left(3^5+3^6+3^7\right)+\left(3^8+3^9+3^{10}\right)\)
\(B=3+3.\left(3+3^2+3^3\right)+3^4\left(3+3^2+3^3\right)+3^7\left(3+3^2+3^3\right)\)
\(B=3+\left(3+3^4+3^7\right)\left(3+3^2+3^3\right)=3+39.\left(3+3^4+3^7\right)\)
ta có \(\left\{{}\begin{matrix}39\left(3+3^4+3^7\right)⋮13\\3⋮̸13\end{matrix}\right.\)
\(\Rightarrow3+39.9\left(3+3^4+3^7\right)⋮̸13\)
\(\Rightarrow B⋮̸13\)
vậy B không chia hết cho 13
đề đúng ko vậy
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