Ramanujan tau

The Ramanujan tau function $\tau \colon \mathbb{N} \rightarrow \mathbb{Z}$ is defined by the formulas $$\displaystyle\sum_{n=1}^{\infty} \tau(n)q^n = q \prod_{n=1}^{\infty} (1-q^n)^{24} = \eta(z)^{24}=\Delta(z),$$ where $q=e^{2\pi i z}$ with $\mathrm{Re}(z)>0$, $\eta$ denotes the Dedekind eta function, and $\Delta$ denotes the discriminant modular form.

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  Plot of $\tau(n)$ for $n=0,1,\ldots,250$.

Properties

Ramanujan tau is multiplicative
Ramanujan tau of a power of a prime
Ramanujan tau inequality