当n=1时
a1=s1=32*1-1*1=31
当n≥2时
an=Sn-S(n-1)
=32n-n²-[32(n-1)-(n-1)²]
=32n-n²-(32n-32-n²+2n-1)
=-2n+33
令an>0,则-2n+33>0
解得:n