Ix(a,b)=xaybB(a,b)(α1β1+α2β2+α3β3+…)α1=1,αm+1=(a+m−1)(a+b+m−1)m(b−m)x2(a+2m−1)2βm+1=m+m(b−m)xa+2m−1+(a+m)(a−(a+b)x+1+m(2−x))a+2m+1