Sn+1+Sn-1=2Sn+1则Sn+1-Sn=Sn-Sn-1+1则乱正烂a(n+1)=an+1所清悔以哗漏an=a1+(n-1)*1=2+n-1=n+1
Sn+1+Sn-1=2Sn+1则Sn+1-Sn=Sn-Sn-1+1则a(n+1)=a(n) +1所卖缓握中庆哪轿以a(n)=a1+(n-1)*1=2+n-1=n+1