Ta có: \(17^2=\left(...9\right)\) ; \(24^4=\left(24^2\right)^2=\left(...6\right)^2=\left(...6\right)\)
\(13^{21}=\left(13^4\right)^5.13=\left(...1\right)^5.13=\left(...1\right).13=\left(...3\right)\)
\(\Rightarrow A=17^2+24^4-13^{21}=\left(...9\right)+\left(...6\right)-\left(...3\right)\)
\(\Rightarrow A=\left(...5\right)-\left(...3\right)\)
\(\Rightarrow A=\left(...2\right)⋮2\)
\(\Rightarrow A⋮2\left(đpcm\right)\)