How to write the relation for a graph in graph theory?

Question

I've been given these graphs and I need to write the relations for them. Could you pleas let me know how this can be done? I can write the edge relations <1,2> <1,4> <1,6>,... but I think something different is being asked here

Answer 1

You have found the pattern in the second one. You say "each node goes to the one above it and the one above that". If $a$ is the start of the arrow and $b$ is the end of the arrow, what does that tell you about the quantity $b-a$? Write that down, and you have your answer. And don't forget to fill in $B = \{1, 2, 3, 4, 5\}$.

The pattern in the first one is divisibility. The arrows point to multiples. Since the drawn in arrows aren't really part of the picture, it gets a little more awkward to describe, but I would maybe go for something like "$a\neq b$ and $a\mid b$", or maybe "$\frac ba$ is an integer larger than $1$". Again, don't forget the $A = \{\_\_\_\}$ field.