

A110409


Number of times repeated reverse concatenation of n followed by n gives a prime, where n == 1,3,7 or 9 (mod 10), or 0 if no such prime exists.


1



1, 0, 0, 0, 0, 10, 3, 7, 0, 3, 0, 10, 3, 0, 22, 0, 51, 7, 9, 10, 0, 412, 0, 16, 18, 0, 3, 0, 3, 3, 0, 9, 0, 3, 0, 3, 4, 0, 3, 0, 0
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OFFSET

0,6


COMMENTS

Except for the first term every nonzero term is >1.
The larger numbers are probable primes.  Joshua Zucker, May 10 2006
The sequence probably continues 0 0 10 0 0 0 0 0 0 4 0 0 0 130 6 0 0 0 4 0 0 0 0 0 6 6 0 0 4 0 4 0 0 0 0 0 10 10 34 0 0 0 0 but the 0's in that list that correspond to 103, 107, 113, 119, 133, 143, 157, 169, 187, 203, 209, are not proved (but if there is a term there, it is more than 500).  Joshua Zucker, May 10 2006
Not only must each nonzero term be >1 (to avoid divisibility by 11), it also cannot equal 2 (mod 3) to avoid divisibility by 3.  Joshua Zucker, May 10 2006


LINKS

Table of n, a(n) for n=0..40.


EXAMPLE

The term corresponding to 19 is 7, as 7 concatenation of 91 followed by 19 is the least such prime. (9191919191919119 is a prime).


CROSSREFS

Cf. A110408.
Sequence in context: A167764 A241887 A182493 * A064211 A050133 A068608
Adjacent sequences: A110406 A110407 A110408 * A110410 A110411 A110412


KEYWORD

base,more,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



