@article{1028997952, author = {Harary, Frank}, title = {The number of oriented graphs.}, journal = {Michigan Math. J.}, volume = {4}, number = {2}, year = {1957}, pages = { 221-224}, language = {en}, url = {http://dml.mathdoc.fr/item/1028997952} }
Harary, Frank. The number of oriented graphs.. Michigan Math. J., Tome 4 (1957) no. 2, pp. 221-224. http://gdmltest.u-ga.fr/item/1028997952/