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A171011
Number of ways to place two non-attacking rooks on all free n-ominoes.
0
0, 0, 1, 9, 48, 242, 1178, 5793, 27651, 131383
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OFFSET
1,4
LINKS
Table of n, a(n) for n=1..10.
EXAMPLE
The triomino XX admits 1 combination of 2 non-attacking rooks.
............ X
CROSSREFS
Sequence in context:
A054460
A115053
A181959
*
A264273
A226751
A073584
Adjacent sequences:
A171008
A171009
A171010
*
A171012
A171013
A171014
KEYWORD
nonn
AUTHOR
David Scambler
, Aug 27 2010
STATUS
approved
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Last modified March 19 04:26 EDT 2024. Contains 370952 sequences. (Running on oeis4.)