Current I is flowing through a regular polygon with n-sides then magnetic field at its center is (polygon is inscribed in a circle of radius r)

$x=\text{r}\cos \left(\frac{\pi }{x}\right)$

$\text{B}=\frac{{\mu }_{0}I}{4\pi x}\left[\sin \left(\frac{\pi }{\text{n}}\right)+\sin \left(\frac{\pi }{\text{n}}\right)\right]$

$=\frac{{\mu }_{0}I}{4\pi x}2.\sin \left(\frac{\pi }{\text{n}}\right)$

$=\frac{{\mu }_{0}I}{4\pi \text{r}\cos \left(\frac{\pi }{\text{n}}\right)}2\sin \left(\frac{\pi }{\text{n}}\right)$

$\text{B}=\frac{{\mu }_{0}I}{2\pi \text{r}}\text{Tan}\left(\frac{\pi }{\text{n}}\right)$

For n sides ${\text{B}}_{\text{net}}=\frac{{\mu }_0\text{n}I}{2\pi \text{r}}\text{Tan}\left(\frac{\pi }{\text{n}}\right)$