For information on 3.14159..., see Pi.

For information on the number-theoretic function pi(n), see NumberTheory[pi].

For the product operator, see product.

$\sin \left(\frac{\mathrm{Pi}}{2}\right)$

$1$

${\mathrm{evalf}}_{20}\left(\mathrm{Pi}\right)$

$3.1415926535897932385$

${\mathrm{NumberTheory}}_{\mathrm{pi}}\left(1000\right)$

$168$

$\prod _{n\=1}^{\mathrm{\∞}}\left(\frac{4n^2}{4n^2-1}\right)$

$\frac{\mathrm{\pi }}{2}$