arithmetic progression in c

Hi guys do have any ideas on how to make this arithmetic progression in c?
n^2 - m^2 - k^2 = aaa (a is any number)
for example 53^2 - 37^2 - 21^2 = 999
I need to find all the possible aaa's here

int n,m,k,a;for(n=0;n<256;n++)for(m=0;m<256;m++)for(k=0;k<256;k++)for(a=0;a<256;a++)assert((pow(n,2)-pow(m,2)-pow(k,2))!=a);