Though I don't know if the formula I've found is useful, I decided to publish it anyway. $$ \text{Arg}( \zeta (z)) = -\sum_ {k = 1}^{\infty}\sum _ {q = 1}^{\infty}\frac {1} {k P_q^{k x}}\text {Sin}( k y \text{ Log}(P_q ) ) \text{ , } |z|>1 $$
where $z=x+i y$ and $p_q$ is th $q^{th}$ prime number.
Here is an example with a plot of $\text{Arg}( \zeta (1+i y))$ in blue, and a plot of the sum in red:

My question is whether the formula is known, whether someone finds it helpful.
EDIT: this post was put 'on hold'. I don't know why. I'm a graphist and foreigner to the mathematics' community, thus it's very hard for me to check the results I got, and this is the reason of this post.
EDIT 2: If someone's interested, this other post shows at the end how the series was calculated simple tools to extract Re, Im, Abs... of any complex function
I have never seen anything like this before. Here is some code for the plot, apparently with a different scale factor: