GAP 4.8.9 installation with standard packages -- copy to your CoCalc project to get it
#g2 f1 6x6 0 1 -1 0 0 0 -1 1 0 0 0 0 -1 1 0 0 -1 1 -1 0 0 1 -1 0 0 0 0 1 -1 0 0 0 -1 1 0 0 6x6 0 0 0 0 0 1 0 -1 0 1 0 0 0 0 0 1 0 0 0 -1 1 1 -1 0 0 0 0 1 -1 0 -1 0 1 0 -1 1 6x6 4 -1 -2 1 1 -2 -1 4 -1 -2 1 1 -2 -1 4 -1 -2 1 1 -2 -1 4 -1 -2 1 1 -2 -1 4 -1 -2 1 1 -2 -1 4 2^5 * 3 * 7 = 672