高一-數列級數問題

求級數和:

1.sigma(k=1~n)k(k+1)(k+2)

2.數列an滿足an+1=an+4n^2，n>=1且a1=1
試求數列an通式(ans:1/3(4n^3-6n^2+2n+3)

3.一數列an滿足a1+2a2+...+nan=n^2+3n+1，n>=1
則a100值為?(ans:101/50)
數列an的通式為?

THANKS!!