Euler phi
From specialfunctionswiki
The Euler phi function is defined as $$\phi(q) = \displaystyle\prod_{k=1}^{\infty} 1-q^k.$$
- Qpochhammer(q,q)infty.png
Plot of $(q,q)_{\infty}$ for $q \in [-1,1]$.
- Complex qpochhammer (q,q) infty.png
Domain coloring of analytic continuation of $(q,q)_{\infty}$ to the unit disk.
