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 A261818 #16 Sep 29 2015 12:31:55
%S A261818 1,313,93139,3931393,11393139311,1113931393111,17111393139311171,
%T A261818 331711139313931117133,3333171113931393111713333,
%U A261818 133331711139313931117133331,1813333171113931393111713333181,1951813333171113931393111713333181591
%N A261818 Minimal nested palindromic primes with seed 1.
%C A261818 Let s be a palindrome and put a(1) = s. Let a(2) be the least palindromic prime having s in the middle; for n > 2, let a(n) be the least palindromic prime have a(n-1) in the middle. Then (a(n)) is the sequence of minimal nested palindromic primes with seed s.
%H A261818 Clark Kimberling, <a href="/A261818/b261818.txt">Table of n, a(n) for n = 1..100</a>
%e A261818 As a symmetric triangle:
%e A261818 ......1
%e A261818 .....313
%e A261818 ....93139
%e A261818 ...3931393
%e A261818 .11393139311
%e A261818 1113931393111
%t A261818 s = {1}; Do[NestWhile[# + 1 &, 1, ! PrimeQ[tmp = FromDigits[Join[#, IntegerDigits[Last[s]], Reverse[#]] &[IntegerDigits[#]]]] &]; AppendTo[s, tmp], {15}]; s
%t A261818 (* _Peter J. C. Moses_, Sep 01 2015 *)
%Y A261818 Cf. A261881 (seed 0 with guide to related sequences).
%K A261818 nonn,easy,base
%O A261818 1,2
%A A261818 _Clark Kimberling_, Sep 17 2015