∫02⁢π∫0πYl1,m1⁡(θ,ϕ)⁢Yl2,m2⁡(θ,ϕ)⁢Yl3,m3⁡(θ,ϕ)⁢sin⁡θ⁢ⅆ⁡θ⁢ⅆ⁡ϕ=((2⁢l1+1)⁢(2⁢l2+1)⁢(2⁢l3+1)4⁢π)12⁢(l1l2l3000)⁢(l1l2l3m1m2m3).