document: The crossing number of P -LRB- N , 3 -RRB- It is proved that the crossing number of the generalized Petersen graph P -LRB- 3k + h , 3 -RRB- is k + h if h in -LCB- 0 , 2 -RCB- and k + 3 if h = 1 , for each k > or = 3 , with the single exception of P -LRB- 9,3 -RRB- , whose crossing number is 2
doc_bio_tags: O B I O O O O O O O O O O O O B I O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O
extractive_keyphrases: crossing number generalized petersen graph