[ Eq(Derivative(x1, t), (1*k21*k6 + (-1)*k21*k7*x1 + (-1)*k21*k8*x5*x1 + (-1)*k21*k9*x5*x1)/k21),
  Eq(Derivative(x2, t), (1*k21*k8*x5*x1 + (-1)*k21*k2*x2 + (-1)*k21*k12*x2 + 1*k21*k11*x4 + (-1)*k21*k13*x6*x2 + (-1)*k21*k17*x16*x2)/k21),
  Eq(Derivative(x3, t), (1*k21*k12*x2 + (-1)*k21*k3*x3 + (-1)*k21*k13*x6*x3 + (-1)*k21*k17*x16*x3)/k21),
  Eq(Derivative(x4, t), (1*k21*k9*x5*x1 + (-1)*k21*k11*x4 + (-1)*k21*k7*x4)/k21),
  Eq(Derivative(x5, t), (1*k21*k4*x3 + (-1)*k21*k5*x5)/k21),
  Eq(Derivative(x6, t), (1*k21*k10*x15 + 1*k21*k14*(x2 + x3)*x6 + (-1)*k21*k16*x6)/k21),
  Eq(Derivative(x7, t), (-1)*k21*k15*x7/k21),
  Eq(Derivative(x8, t), (2*k21*k15*x7 + (-1)*k21*k15*x8)/k21),
  Eq(Derivative(x9, t), (2*k21*k15*x8 + (-1)*k21*k15*x9)/k21),
  Eq(Derivative(x10, t), (2*k21*k15*x9 + (-1)*k21*k15*x10)/k21),
  Eq(Derivative(x11, t), (2*k21*k15*x10 + (-1)*k21*k15*x11)/k21),
  Eq(Derivative(x12, t), (2*k21*k15*x11 + (-1)*k21*k15*x12)/k21),
  Eq(Derivative(x13, t), (2*k21*k15*x12 + (-1)*k21*k15*x13)/k21),
  Eq(Derivative(x14, t), (2*k21*k15*x13 + (-1)*k21*k15*x14)/k21),
  Eq(Derivative(x15, t), (2*k21*k15*x14 + (-1)*k21*k15*x15)/k21),
  Eq(Derivative(x16, t), (1*k21*k20 + 1*k21*k18*(x2 + x3)*x16 + (-1)*k21*k19*x16)/k21) ]