

A110408


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.


2



11, 0, 0, 0, 0, 3131313131313131313113, 71717117, 9191919191919119, 0, 32323223, 0, 9292929292929292929229, 13131331, 0, 7373737373737373737373737373737373737373737337, 0, 14141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141441
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OFFSET

0,1


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, May 10 2006
The Magma Calculator (http://magma.maths.usyd.edu.au/calc/) verified each of the nine nonzero terms as prime.  Jon E. Schoenfield, Aug 24 2009


LINKS

Table of n, a(n) for n=0..16.


CROSSREFS

Cf. A110409.
Sequence in context: A321803 A321797 A113043 * A179920 A216726 A323169
Adjacent sequences: A110405 A110406 A110407 * A110409 A110410 A110411


KEYWORD

base,easy,nonn


AUTHOR

Amarnath Murthy, Jul 30 2005


EXTENSIONS

More terms from Joshua Zucker, May 10 2006
Edited by T. D. Noe, Oct 30 2008


STATUS

approved



