Nonexistence of perfect Steiner triple systems of orders 19 and 21

Reference:

Petteri Kaski. Nonexistence of perfect Steiner triple systems of orders 19 and 21. Bayreuther Mathematische Schriften, 74:130–135, 2005. Proceedings of ALCOMA05, April 3–10, Thurnau, Germany.

Suggested BibTeX entry:

@article{Kaski05b,
    author = {Petteri Kaski},
    journal = {Bayreuther Mathematische Schriften},
    note = {Proceedings of {ALCOMA05}, {A}pril 3--10, {T}hurnau, {G}ermany},
    pages = {130--135},
    title = {Nonexistence of perfect {S}teiner triple systems of orders 19 and 21},
    volume = {74},
    year = {2005},
}