∫0∞tλ-1⁢U⁡(a,b,t)⁢ⅆ⁡t=Γ⁡(λ)⁢Γ⁡(a-λ)⁢Γ⁡(λ-b+1)Γ⁡(a)⁢Γ⁡(a-b+1),