@article{Fredricksen1978a, 
     author = "Fredricksen, Harold and Maiorana, James", 
     doi = "10.1016/0012-365X(78)90002-X", 
     issn = "0012365X", 
     journal = "Discrete Mathematics", 
     link = "http://www.sciencedirect.com/science/article/pii/0012365X7890002X http://linkinghub.elsevier.com/retrieve/pii/0012365X7890002X", 
     month = "jan", 
     number = "3", 
     pages = "207--210", 
     title = "Necklaces of beads in k colors and k-ary de Bruijn sequences", 
     uri = "http://www.sciencedirect.com/science/article/pii/0012365X7890002X", 
     volume = "23", 
     year = "1978", 
}

Problems: 401