yn⁡(z)=-1zn+1⁢∑k=0n(2⁢n-2⁢k-1)!!⁢(12⁢z2)kk!+(-1)n+1zn+1⁢∑k=n+1∞(-12⁢z2)kk!⁢(2⁢k-2⁢n-1)!!.