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A007056
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Let S denote the palindromes in the language {0,1,2}*; a(n) = number of words of length n in the language SS.
(Formerly M2781)
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1
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1, 3, 9, 21, 57, 123, 279, 549, 1209, 2127, 4689, 7989, 17031, 28395, 60615, 98061, 208569, 334563, 705789, 1121877, 2356737, 3718827, 7786359, 12223077, 25488903, 39857523, 82876257, 129135729, 267784119, 416118219, 860825439, 1334448261, 2754778809, 4261609131, 8781196329, 13559714109, 27893530029
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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REFERENCES
| R. Kemp, On the number of words in the language {w in Sigma* | w = w^R }^2, Discrete Math., 40 (1982), 225-234.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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MAPLE
| See A007055.
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CROSSREFS
| Sequence in context: A109755 A005254 A191796 * A026551 A060578 A147078
Adjacent sequences: A007053 A007054 A007055 * A007057 A007058 A007059
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KEYWORD
| nonn
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com), Mira Bernstein, R. Kemp
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EXTENSIONS
| Entry revised by N. J. A. Sloane, Mar 07 2011
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