When the thickness is twice that of 2e, that is, equal to an integer multiple of the wavelength, interference enhancement will occur, resulting in bright fringes.
The wavelength of light in the intermediate medium is λ/n2, which is the second bright stripe, so there is 2e=2 λ/n2.
Due to n3 & gtN2, half-wave loss will occur, minus half a wavelength, 2e=2 λ/n2-0.5 λ/n2.