A123833 - OEIS

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A123833

Number of ways, counted up to symmetry, to build a contiguous building with n LEGO blocks of size 3 X 3 which is symmetric after a rotation by 180 degrees.

1, 1, 9, 22, 317, 980, 13801, 48756, 660997, 2505447 (list; graph; refs; listen; history; text; internal format)

	OFFSET	`1,3`
	LINKS	`Table of n, a(n) for n=1..10.` `M. Abrahamsen and S. Eilers, On the asymptotic enumeration of LEGO structures, Exper Math. 20 (2) (2011) 145-152.` `B. Durhuus and S. Eilers, On the entropy of LEGO, arXiv:math.CO/0504039`
	CROSSREFS	`Sequence in context: A131895 A197498 A113519 * A084023 A156342 A133769` `Adjacent sequences: A123830 A123831 A123832 * A123834 A123835 A123836`
	KEYWORD	`nonn`
	AUTHOR	`Soren Eilers (eilers(AT)math.ku.dk), Oct 29 2006`
	STATUS	`approved`

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Last modified May 18 12:20 EDT 2013. Contains 225419 sequences.