N ν 2 ( x ) ∼ 2 π x ( 1 - 1 2 μ - 3 ( 2 x ) 2 - 1 2 ⋅ 4 ( μ - 1 ) ( μ - 45 ) ( 2 x ) 4 - ⋯ ) {N_{\nu}^{2}}\left(x\right)\sim\frac{2}{\pi x}\left(1-\frac{1}{2}\frac{\mu-3}{(2x)^{2}}-\frac{1}{2\cdot 4}\frac{(\mu-1)(\mu-45)}{(2x)^{4}}-\cdots\right)