A001201 Number of Steiner triple systems (STS's) on 6n+1 or 6n+3 elements.

1, 1, 30, 840, 1197504000, 60281712691200, 1348410350618155344199680000

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn
• nice
• hard
• more

Comments

To be precise, for n even, a(n) is the number of STS's on 3n+1 elements, and for n odd, a(n) is the number of STS's on 3n elements. - Franklin T. Adams-Watters, Apr 10 2010

Examples

			There are 1197504000 STS's on 13 elements.
		

References

• L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 304.
• CRC Handbook of Combinatorial Designs, 1996, p. 70.
• N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
• N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Links

• Petteri Kaski and Patric R. J. Östergård, The Steiner triple systems of order 19, Math. Comp. 73 (2004), 2075-2092.
• Index entries for sequences related to Steiner systems

Crossrefs

Indexed by A047241. Cf. A030128, A030129, A051390.