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A110408
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Smallest prime which is the repeated reverse concatenation of n followed by n ( ending in n), where n == 1,3,7 or 9 (mod 10), or 0 if no such prime exists.
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1
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11, 0, 0, 0, 0, 3131313131313131313113, 71717117, 9191919191919119, 0, 32323223, 0, 9292929292929292929229, 13131331, 0, 7373737373737373737373737373737373737373737337, 0, 14141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141441
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,1
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COMMENTS
| Conjecture: a(n) is 0 iff n is a palindromic prime == 1,3,7 or 9 (mod 10) and/or n ==0 (mod 3). As rev(n) followed by n is == 0 (mod 11), hence every nonzero term contains at least two reverse concatenations of n followed by n.
The larger numbers are probable primes. - Joshua Zucker (joshua.zucker(AT)stanfordalumni.org), May 10 2006
The Magma Calculator (http://magma.maths.usyd.edu.au/calc/) verified each of the nine non-zero terms as prime. [From Jon E. Schoenfield (jonscho(AT)hiwaay.net), Aug 24 2009]
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CROSSREFS
| Cf. A110409.
Sequence in context: A034249 A131679 A113043 * A179920 A138066 A173189
Adjacent sequences: A110405 A110406 A110407 * A110409 A110410 A110411
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KEYWORD
| base,easy,nonn
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AUTHOR
| Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Jul 30 2005
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EXTENSIONS
| More terms from Joshua Zucker (joshua.zucker(AT)stanfordalumni.org), May 10 2006
Edited by T. D. Noe (noe(AT)sspectra.com), Oct 30 2008
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