Ivica Martinjak and  Mario-Osvin Pavcevic,  BIBD-s for (13, 5, 5), (16, 6, 5) and (21, 6, 4) Possessing Possibly an Automorphism of Order 3.   journal   = {International Journal of Mathematical and Computational Sciences}, [online]. World Academy of Science, Engineering and Technology.
    October 2009, vol. 34(10). 846 - 849
    [viewed 11 May 2024]. Available from: https://publications.waset.org/pdf/8987.