S⁡(z)=-cos⁡(12⁢π⁢z2)⁢∑n=0∞(-1)n⁢π2⁢n+11⋅3⁢⋯⁢(4⁢n+3)⁢z4⁢n+3+sin⁡(12⁢π⁢z2)⁢∑n=0∞(-1)n⁢π2⁢n1⋅3⁢⋯⁢(4⁢n+1)⁢z4⁢n+1.