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A007056 Number of words of length n in a certain language.
(Formerly M2781)
+0
1
1, 3, 9, 21, 57, 123, 279, 549, 1209, 2127, 4689 (list; graph; listen)
OFFSET

0,2

REFERENCES

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

R. Kemp, On the number of words in the language {w in Sigma* | w = w^R }^2, Discrete Math., 40 (1982), 225-234.

CROSSREFS

Sequence in context: A111209 A109755 A005254 this_sequence A026551 A060578 A147078

Adjacent sequences: A007053 A007054 A007055 this_sequence A007057 A007058 A007059

KEYWORD

nonn

AUTHOR

N. J. A. Sloane (njas(AT)research.att.com), Mira Bernstein, R. Kemp

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Last modified November 25 20:09 EST 2009. Contains 167514 sequences.


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