login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
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 (list; graph; refs; listen; history; text; internal format)
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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified October 15 13:38 EDT 2019. Contains 328030 sequences. (Running on oeis4.)