Faber F1
From specialfunctionswiki
The Faber function $F_1$ is defined by $$F_1(x)=\displaystyle\sum_{k=1}^{\infty} \dfrac{1}{10^k} \displaystyle\inf_{m \in \mathbb{Z}} \left|2^{k!} x -m \right|.$$
Properties
Faber F1 is continuous
Faber F1 is nowhere differentiable