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A123820 Number of ways, counted up to symmetry, to build a contiguous building with n LEGO blocks of size 2 X 2 which is symmetric after a rotation by 90 degrees. 0
1, 1, 1, 1, 3, 4, 5, 10, 26, 38, 51, 121, 324, 488, 673, 1808 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,5

LINKS

Table of n, a(n) for n=1..16.

CROSSREFS

Cf. A112389, A123762 - A123827, A123829 - A123849.

Sequence in context: A122413 A297661 A136366 * A261903 A133320 A225906

Adjacent sequences:  A123817 A123818 A123819 * A123821 A123822 A123823

KEYWORD

nonn

AUTHOR

Søren Eilers, Oct 29 2006

STATUS

approved

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Last modified April 6 12:08 EDT 2020. Contains 333273 sequences. (Running on oeis4.)