Fℓ⁡(η,ρ)=ρℓ+1⁢2ℓ⁢ⅇⅈ⁢ρ-(π⁢η/2)|Γ⁡(ℓ+1+ⅈ⁢η)|⁢∫01ⅇ-2⁢ⅈ⁢ρ⁢t⁢tℓ+ⅈ⁢η⁢(1-t)ℓ-ⅈ⁢η⁢ⅆ⁡t,