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 A071606 #9 Jul 28 2024 19:44:23
%S A071606 2,131,11311,1114111,111181111,11112721111,1111118111111,
%T A071606 111111151111111,11111112521111111,1111111111111111111,
%U A071606 111111111161111111111,11111111111111111111111,1111111111129211111111111,111111111111212111111111111,11111111111111611111111111111
%N A071606 Smallest zero-free palindromic prime of 2n + 1 digits.
%H A071606 Sean A. Irvine, <a href="/A071606/b071606.txt">Table of n, a(n) for n = 0..100</a>
%t A071606 a[n_] := Block[{k = (10^(n + 1) - 1)/9}, While[m = FromDigits[ Join[ IntegerDigits[k], Reverse[ Drop[ IntegerDigits[k], -1]]]]; !PrimeQ[m], k++ ]; m]; Table[ a[n], {n, 0, 13}]
%Y A071606 Cf. A028989.
%K A071606 nonn,base
%O A071606 0,1
%A A071606 _Lekraj Beedassy_, Jun 21 2002
%E A071606 Edited by _Robert G. Wilson v_, Jun 21 2002
%E A071606 More terms from _Sean A. Irvine_, Jul 28 2024