Factorizar el polinomio a^7+128

/           /pi\          /pi\\ /         2/pi\        2/pi\\ /         2/pi\        2/pi\          /pi\    /pi\\ /         /pi\    /2*pi\        /pi\    /2*pi\          /pi\    /2*pi\          /2*pi\    /pi\\ /           /pi\    /2*pi\        /pi\    /2*pi\          /pi\    /2*pi\          /2*pi\    /pi\\ /         /pi\    /3*pi\        /pi\    /3*pi\          /3*pi\    /pi\          /pi\    /3*pi\\ /         /pi\    /3*pi\        /pi\    /3*pi\          /pi\    /3*pi\          /3*pi\    /pi\\
|a + - 2*cos|--| - 2*I*sin|--||*|a + 2*cos |--| + 2*sin |--||*|a + 2*cos |--| - 2*sin |--| + 4*I*cos|--|*sin|--||*|a + 2*sin|--|*sin|----| - 2*cos|--|*cos|----| - 2*I*cos|--|*sin|----| - 2*I*cos|----|*sin|--||*|a + - 2*cos|--|*cos|----| - 2*sin|--|*sin|----| + 2*I*cos|--|*sin|----| - 2*I*cos|----|*sin|--||*|a + 2*cos|--|*cos|----| + 2*sin|--|*sin|----| + 2*I*cos|----|*sin|--| - 2*I*cos|--|*sin|----||*|a + 2*cos|--|*cos|----| - 2*sin|--|*sin|----| + 2*I*cos|--|*sin|----| + 2*I*cos|----|*sin|--||
\           \7 /          \7 // \          \7 /         \7 // \          \7 /         \7 /          \7 /    \7 // \         \7 /    \ 7  /        \7 /    \ 7  /          \7 /    \ 7  /          \ 7  /    \7 // \           \7 /    \ 7  /        \7 /    \ 7  /          \7 /    \ 7  /          \ 7  /    \7 // \         \7 /    \ 7  /        \7 /    \ 7  /          \ 7  /    \7 /          \7 /    \ 7  // \         \7 /    \ 7  /        \7 /    \ 7  /          \7 /    \ 7  /          \ 7  /    \7 //

$$\left(a + \left(2 \sin^{2}{\left(\frac{\pi}{7} \right)} + 2 \cos^{2}{\left(\frac{\pi}{7} \right)}\right)\right) \left(a + \left(- 2 \cos{\left(\frac{\pi}{7} \right)} - 2 i \sin{\left(\frac{\pi}{7} \right)}\right)\right) \left(a + \left(- 2 \sin^{2}{\left(\frac{\pi}{7} \right)} + 2 \cos^{2}{\left(\frac{\pi}{7} \right)} + 4 i \sin{\left(\frac{\pi}{7} \right)} \cos{\left(\frac{\pi}{7} \right)}\right)\right) \left(a + \left(- 2 \cos{\left(\frac{\pi}{7} \right)} \cos{\left(\frac{2 \pi}{7} \right)} + 2 \sin{\left(\frac{\pi}{7} \right)} \sin{\left(\frac{2 \pi}{7} \right)} - 2 i \sin{\left(\frac{2 \pi}{7} \right)} \cos{\left(\frac{\pi}{7} \right)} - 2 i \sin{\left(\frac{\pi}{7} \right)} \cos{\left(\frac{2 \pi}{7} \right)}\right)\right) \left(a + \left(- 2 \cos{\left(\frac{\pi}{7} \right)} \cos{\left(\frac{2 \pi}{7} \right)} - 2 \sin{\left(\frac{\pi}{7} \right)} \sin{\left(\frac{2 \pi}{7} \right)} - 2 i \sin{\left(\frac{\pi}{7} \right)} \cos{\left(\frac{2 \pi}{7} \right)} + 2 i \sin{\left(\frac{2 \pi}{7} \right)} \cos{\left(\frac{\pi}{7} \right)}\right)\right) \left(a + \left(2 \cos{\left(\frac{\pi}{7} \right)} \cos{\left(\frac{3 \pi}{7} \right)} + 2 \sin{\left(\frac{\pi}{7} \right)} \sin{\left(\frac{3 \pi}{7} \right)} - 2 i \sin{\left(\frac{3 \pi}{7} \right)} \cos{\left(\frac{\pi}{7} \right)} + 2 i \sin{\left(\frac{\pi}{7} \right)} \cos{\left(\frac{3 \pi}{7} \right)}\right)\right) \left(a + \left(- 2 \sin{\left(\frac{\pi}{7} \right)} \sin{\left(\frac{3 \pi}{7} \right)} + 2 \cos{\left(\frac{\pi}{7} \right)} \cos{\left(\frac{3 \pi}{7} \right)} + 2 i \sin{\left(\frac{\pi}{7} \right)} \cos{\left(\frac{3 \pi}{7} \right)} + 2 i \sin{\left(\frac{3 \pi}{7} \right)} \cos{\left(\frac{\pi}{7} \right)}\right)\right)$$

((((((a - 2*cos(pi/7) - 2*i*sin(pi/7))*(a + 2*cos(pi/7)^2 + 2*sin(pi/7)^2))*(a + 2*cos(pi/7)^2 - 2*sin(pi/7)^2 + 4*i*cos(pi/7)*sin(pi/7)))*(a + 2*sin(pi/7)*sin(2*pi/7) - 2*cos(pi/7)*cos(2*pi/7) - 2*i*cos(pi/7)*sin(2*pi/7) - 2*i*cos(2*pi/7)*sin(pi/7)))*(a - 2*cos(pi/7)*cos(2*pi/7) - 2*sin(pi/7)*sin(2*pi/7) + 2*i*cos(pi/7)*sin(2*pi/7) - 2*i*cos(2*pi/7)*sin(pi/7)))*(a + 2*cos(pi/7)*cos(3*pi/7) + 2*sin(pi/7)*sin(3*pi/7) + 2*i*cos(3*pi/7)*sin(pi/7) - 2*i*cos(pi/7)*sin(3*pi/7)))*(a + 2*cos(pi/7)*cos(3*pi/7) - 2*sin(pi/7)*sin(3*pi/7) + 2*i*cos(pi/7)*sin(3*pi/7) + 2*i*cos(3*pi/7)*sin(pi/7))