Trigamma
From specialfunctionswiki
The trigamma function $\psi^{(1)}$ is defined by $$\psi^{(1)}(z)=\dfrac{\mathrm{d}^2}{\mathrm{d}z^2} \log \Gamma(z),$$ where $\log \Gamma$ denotes the loggamma function.
Domain coloring of $\psi^{(1)}$.
