Ackerman函数 A(n,m) 定义如下 -- 有两个独立的整形变量m、n：

A(1,0) = 2                          m = 0, n = 1
A(0,m) = 1                          m >= 0, n = 0
A(n,0) = n + 2                      m = 0, n >= 2
A(n,m) = A(A(n - 1, m), m - 1)      m >= 1, n >= 1