Formula to draw pyramid of circles

Question

I'm trying to create a pyramid of circles to my game, looking similar to this :

But I can't make it print properly. Constantly I'm getting really strange spirals but nothing close to this. Can anyone give me some tip on proper formula ? My window is 600x600, base of pyramid is 8 .

    fields = new Field[BASE*(BASE/2)+4];
    int line_count = BASE;
    int line_tmp = line_count;
    for(int i=0; i< fields.length; i++){
        for( int j=line_tmp; j <= line_count; j++){
            fields[i] = new Field(0, (150+(line_tmp*5)),(600+line_tmp*5));
        }
        line_count--;
        line_tmp = line_count;
    }