Question

1*2+2*3+3*4.+N*(N+1) 用什么公式算啊

Answer 1

1*2+2*3+3*4.+N*(N+1)

=1^2+2^2+……+N^2+1+2+……+N

=N(N+1)(2N+1)/6+(N+1)N/2

=N(N+1)(N/3+1/6+1/2)

=N(N+1)(N+2)/3

2/1+3/2+4/3+……+(n+1)/n

=n+1+1/2+1/3+1/4+……+1/n

=n+lnn+0.5772157

0.5772157为欧拉常数