Fixed in latest revision to be 4 + 12*numNodes + 4*numEdges. Rationale is 4 bytes to represent num nodes, each vertex is 4 bytes for its id, 4 bytes for length of inbound list, 4 bytes for length of outbound list, and 4 bytes for id of each inbound and outbound vertex. If you think of graph as undirected, then instead of 4*numEdges it's 8*numEdges.