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

>>4
better:

long findaaa(long a){
int d=10;
while(1){
  if(a>=d)d*=10;else return a*d+a*d*d+a*d*d*d;}}

long n,m,k,a;
for(n=1;n<256;n++)
for(m=1;m<256;m++)
for(k=1;k<256;k++)
for(a=1;a<256;a++)
assert((pow(n,2)-pow(m,2)-pow(k,2))!=(findaaa(a)));