Helium ion transition with wavelength near H-alpha line

[matpo39]

here is the question I am stuck on:
Radiation from a helium ion He+ is nearly equal to the wavelength to the $$H_\alpha$$ line (the first line of the Balmer series). (a) Between what states (values of n) does the transition in the helium ion occur? (b) is the wavelength greater or smaller than that of the $$H_\alpha$$ line?

my first attempt to solve this was to use the eqation

$$\frac{1}{\lambda}=R(\frac{1}{n_f^2}-\frac{1}{n_i^2})$$

and i would set $$\lambda = 6562.8 \AA$$the wave length of $$H_\alpha$$ but i still can't solve for because both of the states are unknown. anyone have any suggestions on this?

thanks

 

[quantumdude]

You know that $n_f$ and $n_i$ both have to be natural numbers (1,2,3,...). You can start by trying combinations.