Rydberg’s formula is given as
\(\frac{hc}{\lambda} = 21.76 \times 10^{-19}(\frac{1}{n_1^2}-\frac{1}{n_2^2})\)
h = 6.6 x 10-34 is the plank's constant.
c = 3 x 108 is speed of life.
The shortest wavelength present in the Paschen series of the spectral lines is given for values n1 = 3 and n2 = \(\infty\)
From the above values,
\(\lambda = 819nm\)