G(n+ 1)/G(n)& lt; When 1, the latter term is smaller than the former term, and n is greater than 3.7, that is to say, because n=4, each term is smaller than the former term, which is monotonically decreasing. Then when n= 1, 2, 3, the latter term is greater than the former term, which is monotonically increasing.
Max {G(3), G(4)} indicates that the maximum value is G(3) or G(4).