题有问题吧 按前三项的规律来看应该是求1*2+2*3+3*4+...+n（n+1）才对吧。。n(n+1)=n²+n∴原式=(1²+2²+……+n²)+(1+2+……+n)=n(n+1)(2n+1)/6+n(n+1)/2=n(n+1)(n+2)/3
Sn=sigma(n)-n*(n+1)/2=n*(n+1)*(2n+1)/6
