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A001201 Steiner triple systems (STS's) on 6n+1 or 6n+3 elements.
(Formerly M5214 N2268)
8
1, 1, 30, 840, 1197504000, 60281712691200, 1348410350618155344199680000 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

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. [From Franklin T. Adams-Watters, Apr 10 2010]

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

Table of n, a(n) for n=0..6.

P. Kaski and P. R. J. \"Osterg{\aa}rd (Patric.Ostergard(AT)hut.fi), The Steiner triple systems of order 19

Index entries for sequences related to Steiner systems

EXAMPLE

There are 1197504000 STS's on 13 elements.

CROSSREFS

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

Sequence in context: A160269 A049394 A143169 * A007850 A162833 A163208

Adjacent sequences:  A001198 A001199 A001200 * A001202 A001203 A001204

KEYWORD

nonn,nice,hard,more

AUTHOR

N. J. A. Sloane.

STATUS

approved

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Last modified October 23 14:38 EDT 2014. Contains 248465 sequences.