[ Eq(Derivative(x1, t), (1*k21*2060/365 + (-1)*k21*1/(2*365)*x1 + (-1)*k21*45685/(439197*30)*x1*x2)/k21),
  Eq(Derivative(x2, t), (1*k21*45685/(439197*30)*x1*x2 + (-1)*k21*45682/(439197*30)*x2 + (-1)*k21*1/(2*365)*x2)/k21),
  Eq(Derivative(x3, t), (1*k22*237/10*k20/365000 + (-1)*k22*1/(346/5*365)*x3 + (-1)*16/(108*1000000*1825/2)*x3*x2)/k22),
  Eq(Derivative(x4, t), (1*16/(108*1000000*1825/2)*x3*x2 + (-1)*k22*6/(108*1000000*1825/2)*x4 + (-1)*k22*1/(346/5*365)*x4)/k22) ]