[ Diff(x[1], t) = (1*k[21]*2060/365 + (-1)*k[21]*1/(2*365)*x[1] + (-1)*k[21]*45685/(439197*30)*x[1]*x[2])/k[21],
  Diff(x[2], t) = (1*k[21]*45685/(439197*30)*x[1]*x[2] + (-1)*k[21]*45682/(439197*30)*x[2] + (-1)*k[21]*1/(2*365)*x[2])/k[21],
  Diff(x[3], t) = (1*k[22]*237/10*k[20]/365000 + (-1)*k[22]*1/(346/5*365)*x[3] + (-1)*16/(108*1000000*1825/2)*x[3]*x[2])/k[22],
  Diff(x[4], t) = (1*16/(108*1000000*1825/2)*x[3]*x[2] + (-1)*k[22]*6/(108*1000000*1825/2)*x[4] + (-1)*k[22]*1/(346/5*365)*x[4])/k[22] ]