I think it is more appropriate for you to apply for online courses. You can listen and learn repeatedly to consolidate and improve the learning effect. Moreover, New Oriental Online Postgraduate Mathematics has a one-stop answering system, and any problems can be solved immediately. Answer questions in writing every day, answer questions by phone every week, and discuss and answer questions every half month. Awesome ~
Test and analysis: From the nature of N(x), we can know that when x is odd, the largest odd factor of x is obviously itself. So N(x)=x, so we can decompose and calculate the s