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A001201 Steiner triple systems (STS's) on 6n+1 or 6n+3 elements.
(Formerly M5214 N2268)

%I M5214 N2268

%S 1,1,30,840,1197504000,60281712691200,1348410350618155344199680000

%N Steiner triple systems (STS's) on 6n+1 or 6n+3 elements.

%C 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

%D L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 304.

%D CRC Handbook of Combinatorial Designs, 1996, p. 70.

%D N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

%H Petteri Kaski and Patric R. J. Östergård, <a href="http://dx.doi.org/10.1090/S0025-5718-04-01626-6">The Steiner triple systems of order 19</a>, Math. Comp. 73 (2004), 2075-2092.

%H <a href="/index/St#Steiner">Index entries for sequences related to Steiner systems</a>

%e There are 1197504000 STS's on 13 elements.

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

%K nonn,nice,hard,more

%O 0,3

%A _N. J. A. Sloane_

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Last modified May 7 09:23 EDT 2021. Contains 343645 sequences. (Running on oeis4.)