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A050683
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Number of palindromes of length n.
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13
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9, 9, 90, 90, 900, 900, 9000, 9000, 90000, 90000, 900000, 900000, 9000000, 9000000, 90000000, 90000000, 900000000, 900000000, 9000000000, 9000000000, 90000000000, 90000000000, 900000000000, 900000000000, 9000000000000
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| In general the number of base k palindromes with n digits is (k-1)*k^floor[(n-1)/2].
This sequence does not count 0 as palindrome with 1 digit, see A070252=(10,9,90,90...) for the variant which does. [From M. F. Hasler (www.univ-ag.fr/~mhasler), Nov 16 2008]
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LINKS
| Vincenzo Librandi, Table of n, a(n) for n = 1..1000
Dr. Math, More info 1.
Dr. Math, More info 2.
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FORMULA
| a(n) = 9*10^floor[(n-1)/2]
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PROG
| (PARI) A050683(n)=9*10^((n-1)\2) [From M. F. Hasler (www.univ-ag.fr/~mhasler), Nov 16 2008]
(MAGMA) [9*10^Floor((n-1)/2): n in [1..30]]; // Vincenzo Librandi, Aug 16 2011
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CROSSREFS
| Cf. A002113, A050250, A050251, A070252, A070199. Cf. A016116 for numbers of binary palindromes, A016115 for prime palindromes.
Sequence in context: A112296 A038299 A165427 * A092548 A121389 A065242
Adjacent sequences: A050680 A050681 A050682 * A050684 A050685 A050686
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KEYWORD
| nonn,easy,base,nice
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AUTHOR
| Patrick De Geest (pdg(AT)worldofnumbers.com), Aug 15 1999.
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EXTENSIONS
| Additional comments from Henry Bottomley (se16(AT)btinternet.com), Aug 14 2000
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