\[\frac{3n^{3} + 4n^{2} + 162}{n^{2}} =\]
\[= \frac{n^{2}(3n + 4) + 162}{n^{2}} =\]
\[= \frac{n^{2}(3n + 4)}{n^{2}} + \frac{162}{n^{2}} =\]
\[= 3n + 4 + \frac{162}{n^{2}}\]
\[\Longrightarrow n^{2} = 1;9 \Longrightarrow n = \pm 1;\ \pm 3.\]