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 A261826 #8 Sep 29 2015 12:49:54
%S A261826 9,191,71917,147191741,3914719174193,139147191741931,
%T A261826 7213914719174193127,33721391471917419312733,
%U A261826 9337213914719174193127339,1719337213914719174193127339171,11171933721391471917419312733917111,1111719337213914719174193127339171111
%N A261826 Minimal nested palindromic primes with seed 9.
%C A261826 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 A261826 Clark Kimberling, <a href="/A261826/b261826.txt">Table of n, a(n) for n = 1..200</a>
%e A261826 As a triangle:
%e A261826 .......9
%e A261826 ......191
%e A261826 .....71917
%e A261826 ...147191741
%e A261826 .3914719174193
%e A261826 139147191741931
%t A261826 s = {9}; Do[NestWhile[# + 1 &, 1, ! PrimeQ[tmp = FromDigits[Join[#, IntegerDigits[Last[s]], Reverse[#]] &[IntegerDigits[#]]]] &]; AppendTo[s, tmp], {15}]; s
%t A261826 (* _Peter J. C. Moses_, Sep 01 2015 *)
%Y A261826 Cf. A261881 (seed 0, with guide to related sequences).
%K A261826 nonn,easy,base
%O A261826 1,1
%A A261826 _Clark Kimberling_, Sep 23 2015