 1             3                 0 ->    6

      2             9                 6 ->   12

      3            15                12 ->   18

      4            21                18 ->   24

      5            27                24 ->   30

      6            33                30 ->   36

      7            39                36 ->   42

      8            45                42 ->   48

      9            51                48 ->   54

      10            57                54 ->   60

      11            63                60 ->   66

      12            69                66 ->   72

      13            75                72 ->   78

      14            81                78 ->   84

      15            87                84 ->   90

      16            93                90 ->   96

      17            99                96 ->  102

      18           105               102 ->  108

      19           111               108 ->  114