数列求通项问题

貌似等号右边的2的n+1次方而不是2的n次方再加1，修正的结果如下：

An+1 = 4An + 2^(n+1)

An+1 +2^(n+1)= 4An + 2^(n+2)= 4*(An+2^n)

An + 2^n 为等比数列

An + 2^n = (A1 + 2)*4^(n-1)

An = A1*4^(n-1) + 2^(2n-1) -2^n

An+1 + 2^n + 1/3 = 4(An + 2^n-1 + 1/3)
=....
=4^n ( A1+1+1/3)