Is the black number on the clock?
Yes, the number is on the clock.
    src        edge_attr  dst
0     0  to the right of   16
1     0               on    7
2     1               on    7
3     2   to the left of   15
4     2   to the left of    4
5     3  to the right of   18
6     4  to the right of    2
7     4   to the left of    8
8     8  to the right of    4
9    13   to the left of   17
10   14  to the right of   19
11   15  to the right of    2
12   16   to the left of    0
13   17  to the right of   13
14   18   to the left of    3
15   18               on    7
16   19   to the left of   14