\[\boxed{\text{4.\ 386}}\]
\[\textbf{а)} - |n|\]
\[при\ n = 0.\ \]
\[\textbf{б)}\ 3 - |n|\]
\[при\ n = 0.\]
\[\textbf{в)} - |n - 1|\]
\[при\ n = 1.\]
\[\textbf{г)} - |n - 3|\]
\[при\ n = 3.\]
\[\textbf{д)} - (n - 1)^{2}\]
\[при\ n = 1.\ \]