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Search: id:A121907
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| A121907 |
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G.f.: (1+x+x^2)/(1-2*x-2*x^2) |
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+0
1
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| 1, 3, 9, 24, 66, 180, 492, 1344, 3672, 10032, 27408, 74880, 204576, 558912, 1526976, 4171776, 11397504, 31138560, 85072128, 232421376, 634987008, 1734816768, 4739607552, 12948848640, 35376912384, 96651522048, 264056868864, 721416781824, 1970947301376
(list; graph; listen)
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OFFSET
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0,2
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REFERENCES
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A. Burstein and T. Mansour, Words restricted by 3-letter ..., Annals. Combin., 7 (2003), 1-14.
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LINKS
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Index entries for sequences related to linear recurrences with constant coefficients
A. Burstein and T. Mansour, Words restricted by 3-letter ....
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FORMULA
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a(0)=1, a(1)=3, a(2)=9, a(n)=2*a(n-1)+2*a(n-2) for n>2. [From Philippe DELEHAM (kolotoko(AT)wanadoo.fr), Sep 19 2009]
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CROSSREFS
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Sequence in context: A153582 A096168 A051042 this_sequence A118771 A091587 A018047
Adjacent sequences: A121904 A121905 A121906 this_sequence A121908 A121909 A121910
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KEYWORD
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nonn
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com), Nov 20 2006
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