how to factorize 2x^n+1 - 5x^n - 3^n-1 ?

請問各下有沒有打少了一個x, 應該是2x^n+1 - 5x^n - 3x^n-1 不是 2x^n+1 - 5x^n - 3^n-1
如果是2x^n+1 - 5x^n - 3x^n-1 ,答案是x^(n-1)(2x+1)(x-3)
如果是2x^n+1 - 5x^n - 3^n-1 , 則不能計算.

2x^n+1 - 5x^n - 3^n - 1
= x^n-1 (2x^2 - 5x - 3)
= x^n-1 (2x + 1) (x - 3)