> 那为什么9!=1!+2!+3!而不加0!,产生'no'啊??
For a given n, you'll check if there are some xi, and let n equal to 
Σ(1<=i<=t)xi!. (t >=1 1, xi >= 0, xi = xj iff. i = j). 
x1, x2...xt是任意的可以是3，2，....5