\(S=1+5+5^2+5^3+5^4+...+5^{2010}\)
\(\Leftrightarrow S=1+\left(5+5^2\right)+\left(5^3+5^4\right)+....+\left(5^{2009}+5^{2010}\right)\)
\(\Leftrightarrow S=1+5\left(1+5\right)+5^3\left(1+5\right)+....+5^{2009}\left(1+5\right)\)
\(\Leftrightarrow S=1+5\cdot6+5^3\cdot6+...+5^{2009}\cdot6\)
\(\Leftrightarrow S=1+6\left(5+5^3+...+5^{2009}\right)\)
Mà \(6\left(5+5^3+....+5^{2009}\right)⋮2\)
=> S chia 2 dư 1