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