This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A110408 #14 Jul 06 2019 14:20:27 %S A110408 11,0,0,0,0,3131313131313131313113,71717117,9191919191919119,0, %T A110408 32323223,0,9292929292929292929229,13131331,0, %U A110408 7373737373737373737373737373737373737373737337,0,14141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141441 %N 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. %C A110408 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. %C A110408 The larger numbers are probable primes. - _Joshua Zucker_, May 10 2006 %C A110408 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 %Y A110408 Cf. A110409. %K A110408 base,easy,nonn %O A110408 0,1 %A A110408 _Amarnath Murthy_, Jul 30 2005 %E A110408 More terms from _Joshua Zucker_, May 10 2006 %E A110408 Edited by _T. D. Noe_, Oct 30 2008