C

n=sqrt(1+21.1/(1-pow(1.37/x,2)))

Python

n=(1+21.1/(1-(1.37/x)**2))**.5

Fortran

n=SQRT(1+21.1/(1-(1.37/x)**2))

MATLAB

n=sqrt(1+21.1./(1-(1.37./x).^2))

LaTeX

n^2-1=\frac{21.1λ^2}{λ^2-1.37^2}