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.

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

$1$

$\mathrm{evalf}\left[20\right]\left(\mathrm{\pi }\right)$

$3.1415926535897932385$

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

$168$

$\mathrm{product}\left(\frac{4n^2}{4n^2-1}\,n=1..\mathrm{\infty }\right)$

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