có 1 sự đúng nhẹ

\(1+2^2+2^4+...+2^{50}\)

\(=\left(1+2^2+2^4\right)+\left(2^6+2^8+2^{10}\right)+...+\left(2^{46}+2^{48}+2^{50}\right)\)

\(=21+2^6\left(1+2^2+2^4\right)+...+2^{46}\left(1+2^2+2^4\right)\)

\(=1.21+2^6.21+...+2^{46}.21\)

\(=7.3.\left(1+2^6+...+2^{46}\right)\)chia hết cho 7