\(n=5^0+5^1+...+5^{2019}\)
\(n=\left(5^0+5^3\right)+\left(5^1+5^4\right)+...+\left(5^{2016}+5^{2019}\right)\)
\(n=\left(5^0+5^3\right)+5\left(5^0+5^3\right)+...+5^{2016}\left(5^0+5^3\right)\)
\(n=126+5\cdot126+...+5^{2016}\cdot126\)
\(n=126\left(1+5+...+5^{2016}\right)⋮126\) (đpcm)
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\(n=5^0+5^1+...+5^{2019}\)
\(n=5^0+\left(5^1+5^2\right)+...+\left(5^{2017}+5^{2018}\right)+5^{2019}\)
\(n=5^0+\left(5^1+5^2\right)+...+5^{2016}\left(5^1+5^2\right)+5^{2019}\)
\(n=5^0+30+...+5^{2016}\cdot30+5^{2019}\)
\(n=5^0+30\left(1+5^2+...+5^{2016}\right)+5^{2019}\)
Đến đây bí =))
Cbht