1 ] 2 = 1  3 3 = 4  15 4 = 5 + 6 + 7 + 8 + 9 + 13 5 6 7 8 9 10 11 12 13 14 15 = 16 + 17 + 18 + 19 + 20 + 22 16 17 18 19 20 21 22 23 = 16 + 17 + 18 + 20 23 = 25 + 26 + 27 23 = 2  1 + 4  19  22 24 25 26 27