GAP 4.8.9 installation with standard packages -- copy to your CoCalc project to get it
#g2 f3 z3 c3 6x 6 0 0 0 0 0 1 -1 0 0 0 0 1 0 -1 0 0 0 1 0 0 -1 0 0 1 0 0 0 -1 0 1 0 0 0 0 -1 1 6x 6 0 0 0 0 0 1 0 0 0 0 1 0 0 0 0 1 0 0 0 0 1 0 0 0 0 1 0 0 0 0 1 0 0 0 0 0 6x 6 6 -1 -1 -1 -1 -1 -1 6 -1 -1 -1 -1 -1 -1 6 -1 -1 -1 -1 -1 -1 6 -1 -1 -1 -1 -1 -1 6 -1 -1 -1 -1 -1 -1 6 6x 6 2 -1 0 0 0 0 -1 2 -1 0 0 0 0 -1 2 -1 0 0 0 0 -1 2 -1 0 0 0 0 -1 2 -1 0 0 0 0 -1 2 6x 6 4 -1 -1 0 0 -1 -1 4 -1 -1 0 0 -1 -1 4 -1 -1 0 0 -1 -1 4 -1 -1 0 0 -1 -1 4 -1 -1 0 0 -1 -1 4 6d0 % zentr -1 6 % zentr 0 1 0 0 0 -1 0 1 1 0 0 -1 -1 1 1 1 0 -1 -1 0 1 1 1 -1 -1 0 0 1 1 0 -1 0 0 0 1 0 6 % zentr 0 0 1 0 -1 0 0 0 1 1 -1 -1 0 0 1 1 0 -1 -1 0 1 1 0 0 -1 -1 1 1 0 0 0 -1 0 1 0 0 6d0 % cen -1 6 % cen 0 1 0 0 0 -1 0 1 1 0 0 -1 -1 1 1 1 0 -1 -1 0 1 1 1 -1 -1 0 0 1 1 0 -1 0 0 0 1 0 6 % cen 0 0 1 0 -1 0 0 0 1 1 -1 -1 0 0 1 1 0 -1 -1 0 1 1 0 0 -1 -1 1 1 0 0 0 -1 0 1 0 0 2^2 * 7^1 = 28 %order of the group