W_{4,18}=1 + alpha*y^6 + (2754 - 6*alpha)*y^8 + (18360 + 15*alpha)*y^10 + (77112 - 20*alpha)*y^12 + (110160 + 15*alpha)*y^14 + (50949 - 6*alpha)*y^16 + (2808 + alpha)*y^18