how to insert double summation in the following equation

my whole formula is

C(i,j+1)=-e(i+1)C(i+1,j)-fC(i,j)+Dsummation(r=0 to k)summation(s=0 to h) (M^s/s!)*(k+1)(k+2)C(k+2,h-s)

the code wrote is as follows . First i initial the value with the help of first for loop

for i=1:1:n+5
    C1(1,1)=0.030792+0.009208;
    C1(i,1)=(0.009208*((-0.00000588235)^(i-1))/factorial(i-1));

end

then my second for loop is to calculate C(0,1),C(1,1),......,C(0,2),C(1,2).....Now i am not getting how to include the double summation term as mention in the above formula

for j=1:1:n+1
  for  i=1:1:n+1
    C1(i,j+1)=(a*i*C1(i+1,j)-b*C1(i,j)+c*(C2(i,j)-C1(i,j))+D1*i*(i+1)*C1(i+2,j))/j;
      end
end