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A334457 Block sizes k of nontrivial biplanes. 1
4, 5, 6, 9, 11, 13, 16 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

A biplane is an incidence structure consisting of a set P of h points and a set of h blocks, each of which is an k-subset of P (block size k), such that every pair of points lies in exactly 2 blocks (see Alavi et al.).

LINKS

Table of n, a(n) for n=1..7.

Seyed Hassan Alavi, Ashraf Daneshkhah, Cheryl E Praeger, Symmetries of biplanes, arXiv:2004.04535 [math.GR], 2020. See Introduction p. 1.

P. Kaski and P. R. J. Östergård. There are exactly five biplanes with k = 11, J. Combin. Des., 16(2):117-127, 2008.

CROSSREFS

Cf. A001109, A003409, A038723, A038725, A054490, A334456 (h).

Sequence in context: A242040 A206822 A195993 * A010456 A072496 A306482

Adjacent sequences:  A334454 A334455 A334456 * A334458 A334459 A334460

KEYWORD

nonn,more

AUTHOR

Stefano Spezia, Apr 30 2020

STATUS

approved

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Last modified October 25 05:57 EDT 2021. Contains 348239 sequences. (Running on oeis4.)