\(a=3^{2019}.7^{2010}.13^{2011}\)
\(a=3^3.3^{2016}.7^2.7^{2008}.13^3.13^{2008}\)
\(a=27.\left(3^4\right)^{504}.49\cdot\left(7^4\right)^{502}.2197.\left(13^4\right)^{502}\)
\(a=\left(27.49.2197\right).\left(\overline{....1}\right)^{504}.\left(\overline{....1}\right)^{502}.\left(\overline{....1}\right)^{502}\)
\(a=\left(\overline{....1}\right).\left(\overline{....1}\right).\left(\overline{....1}\right).\left(\overline{....1}\right)=\left(\overline{....1}\right)\)
Vậy chữ số hàng đơn vị của số a là 1