0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20
0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19
0,4,8,12,16,20
0,4,8,12,16