kei⁡x=-ln⁡(12⁢x)⁢bei⁡x-14⁢π⁢ber⁡x+∑k=0∞(-1)k⁢ψ⁡(2⁢k+2)((2⁢k+1)!)2⁢(14⁢x2)2⁢k+1.