Question

已知an=n^2+3n+1,求Sn

Answer 1

(1)1^2+2^2+3^2+.+n^2=n(n+1)(2n+1)/6

(2)3*1+3*2+3*3+.+3*n=3n(n+1)/2

(3)1+1+1+.+1(n个)=n

Sn=n(n+1)(2n+1)/6+3n(n+1)/2+n