... of order 9 is the system having an automorphismgroup of order 432, and the other two STS(19) with 12 subsystems of order 7 are the systems having automorphism groups of orders 108 and 144. The ... Nonexistence of perfect Steiner triple systems of orders 19 and 21, Bayreuth.Math. Schr. 74 (2005), 130 135.[26] P. Kaski and P. R. J.ăOstergard, The Steiner triple systems of order 19, Math. ... called blocks or triple s , with the property that every2-subset of points occurs in exactly one block. The size of the point set, v := |X|, is the order of the design, and an STS of order v is commonly...