Hello! Please, could you help me to calculate such a sum
Sum[F[x_1,x_2,...,x_n],{x_1,0,i},{x_2,0,i},...,{x_n,0,i}]
for any positive and integer n? Also, in order to do this I need to build this function, because it is actually something like that
F[f[Sum[x_i,{i,1,n}]],x_1,x_2,a,b,c].
Is it right to write it in this form
F[f[Sum[x_i,{i,1,n}]]]
