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A050251
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Number of palindromic primes less than 10^n.
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2
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4, 5, 20, 20, 113, 113, 781, 781, 5953, 5953, 47995, 47995, 401696, 401696, 3438339, 3438339, 30483565, 30483565, 269577430, 269577430, 2427668363, 2427668363
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,1
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COMMENTS
| Every palindrome with an even number of digits is divisible by 11 and therefore is composite (not prime). Hence there is only one palindromic prime with an even number of digits. - Martin Renner (martin.renner(AT)gmx.net), Apr 15 2006
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LINKS
| P. De Geest, World!Of Palindromic Primes, Page 1
Eric Weisstein's World of Mathematics, Link to a section of The World of Mathematics.
Index entries for sequences related to numbers of primes in various ranges
Shyam Sunder Gupta, Palindromic Primes up to 10^19.
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FORMULA
| a(n) =~ A070199(n)/Ln(10^n) = 1/Ln(10^n)*Sum {k=1..n} 9*10^floor[(k-1)/2]. [From Robert G. Wilson v (rgwv(AT)rgwv.com), May 31 2009]
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CROSSREFS
| Cf. A016115, A002385.
Sequence in context: A042835 A193964 A099897 * A125995 A080610 A047175
Adjacent sequences: A050248 A050249 A050250 * A050252 A050253 A050254
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KEYWORD
| nonn,hard,nice,base
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AUTHOR
| Eric Weisstein (eric(AT)weisstein.com)
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EXTENSIONS
| More terms from Patrick De Geest (pdg(AT)worldofnumbers.com), 8/99.
2 more terms from Shyam Sunder Gupta (guptass(AT)rediffmail.com), Feb 12 2006
2 More terms from Shyam Sunder Gupta (guptass(AT)rediffmail.com), Mar 13 2009
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