回答：N*(N+1)*(N+2)*(N+3)+1
=N*(N+3)*(N+1)*(N+2)+1
=(N^2+3N)*(N^2+3N+2)+1
=(N^2+3N)^2+2(N2+3N)+1
=(N^2+3N+1)^2
为N^2+3N+1的平方