Phi15(x) = x^8-x^7+x^5-x^4+x^3-x+1 Phi15(-2^3^m) = 256^3^m+128^3^m-32^3^m-16^3^m-8^3^m+2^3^m+1 0 1 2 3 4 5 6 7 8 9