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 A261820 #11 Oct 02 2015 13:06:06
%S A261820 111,1311131,113111311,91131113119,9911311131199,12991131113119921,
%T A261820 771299113111311992177,1077129911311131199217701,
%U A261820 11107712991131113119921770111,101110771299113111311992177011101,107101110771299113111311992177011101701
%N A261820 Minimal nested palindromic primes with seed 111.
%C A261820 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 having a(n-1) in the middle. Then (a(n)) is the sequence of minimal nested palindromic primes with seed s.
%H A261820 Clark Kimberling, <a href="/A261820/b261820.txt">Table of n, a(n) for n = 1..200</a>
%e A261820 As a triangle:
%e A261820 111
%e A261820 1311131
%e A261820 113111311
%e A261820 91131113119
%e A261820 9911311131199
%e A261820 12991131113119921
%e A261820 771299113111311992177
%t A261820 s0 = "111"; s = {ToExpression[s0]};Do[NestWhile[# + 1 &, 1, ! PrimeQ[tmp = FromDigits[Join[#, IntegerDigits[Last[s], 10, Max[StringLength[s0],Length[IntegerDigits[Last[s]]]]], Reverse[#]]&[IntegerDigits[#]]]] &]; AppendTo[s, tmp], {10}]; s0 <> ", " <> StringTake[ToString[Rest[s]], {2, -2}]
%t A261820 (* _Peter J. C. Moses_, Sep 23 2015 *)
%Y A261820 Cf. A261881.
%K A261820 nonn,base,easy
%O A261820 1,1
%A A261820 _Clark Kimberling_, Sep 24 2015