This is a $$\infty \frac{x^3}{e^x-1}$$ with few symbols.

Eq 1,

$$$\int_0^\infty \frac{x^3}{e^x-1}\,dx = \frac{\pi^4}{15} \label{eq:sample}$$$

Eq 2 without starting with beginning equation tagger,

$\Gamma(z) = \int_0^\infty t^{z-1}e^{-t}dt\,.$