User blog comment:Syst3ms/A formal interpretation of Y sequence : F sequence/@comment-35470197-20190810061448/@comment-35470197-20190811214725

Then how do you expand S=1,2,4,8,2,4,8? Is it expanded in the following way?
 * 4: S_1=1,2,4,8,2,4,8
 * 4.1: j=6, S_{1,6}-S_{1,7}=4
 * 4.3.3: S_2=1,2,4,1,2,4
 * 4.3.4: Go back to 4.1
 * 4.1: j=5, S_{2,6}-S_{2,5}=2
 * 4.3.1.1: S_{2,3}=undefined