1.Sn=n^2-13n+1,
Sn-1=(n-1)^2-13(n-1)+1,
an=Sn-Sn-1=n^2-13n+1-(n-1)^2+13(n-1)-1=2n-14;
2.由an=2n-14可知,当n=7时,数列为0,前6项为负,故sn有最小值=S7=7*7-13*7+1=-41