Stirling's approximation

James Stirling (1692-1770, Scotland)

$\left.\ln N!\right.=\ln 1+\ln 2+\ln 3+...+\ln N$

Failed to parse (Conversion error. Server ("https://wikimedia.org/api/rest_") reported: "Cannot get mml. Server problem."): {\displaystyle ~=\sum _{k=1}^{N}\ln k}

$~\approx \int _{1}^{N}\ln xdx$

$~=\left[x\ln x-x\right]_{1}^{N}$

$~=N\ln N-N+1$

Thus, for large N

Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \ln N! \approx N \ln N -N}