Akiyama, K., Ogawa, M., & Suetake, C. (2009). On ${\rm STD}_6[18,3]$’s and ${\rm STD}_7[21,3]$’s Admitting a Semiregular Automorphism Group of Order 9. The Electronic Journal of Combinatorics, 16(1), R148. https://doi.org/10.37236/237