A = \(3^{2001}\cdot7^{2002}\cdot13^{2003}\)
A = \(3^{2000}\cdot3\cdot\left(7^2\right)^{1001}\cdot13^{2002}\cdot13\)
A = \(\left(3^2\right)^{1000}\cdot3\cdot49^{1001}.\left(13^2\right)^{1001}.13\)
A = \(9^{1000}\cdot3\cdot\left(...9\right).\left(...9\right)^{1001}.13\)
A = \(\left(...1\right)\cdot3\cdot\left(...9\right)\cdot\left(...9\right)\cdot13\)
A = \(\left(...9\right)\)
Vậy A có chữ số hang đon vị là 9