User blog comment:MilkyWay90/Extension to the Up-Arrow Notation/@comment-2001:56A:71A8:5F00:B9C6:E1DF:6071:32A0-20180605041840

F(a,a,a,2) = F(a,a,F(a,a,a)) = f_w(f_w(a))

F(a,a,a,3) = F(a,a,F(a,a,a,2)) = f_w^3(a)

F(a,a,a,a) = f_w+1(a)

F(a,a,a,a,2) = f_w+1(f_w+1(a))

F(a,a,a,a,a) = f_w+2(a)

the limit is w*2