The following definite integral problem was posted on stackexchange.com today.
\[\begin{equation} 1.35 \times10^-7\int e^{-0.03x}x^4dx
\tag{1}
\end{equation}\]
The version of the gamma function, a useful function for solving improper integrals, that I learned as an undergraduate physics major is
\[\begin{equation}
\int_{0}^{\infty} e^{-x}x^ndx = n!