因为Sn = 2n^2+n-1
所以An = Sn - S(n-1)
= 2n^2 + n - 1 - 2(n-1)^2 - (n-1) + 1
= 4n - 1
当n=1时,A1 = S1 = 2+1-1=2
所以通项公式为：
An = 2 (n=1时)
4n-1 (n>1时)