x^8+x^6+x^4+x^2+1 =(x^2-1)(x^8+x^6+x^4+x^2+1)/(x^2-1) =(x^10-1)/(x^2-1) =(x^5+1)(x^5-1)/(x^2-1) =(x+1)(x^4+x^3-x+1)(x-1)(x^4+x^3+x^2+x+1)/(x^2-1) =(x^4+x^3-x+1)(x^4+x^3+x^2+x+1)
