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 A117702 #10 Feb 16 2025 08:33:00
%S A117702 2,3,5,131,212,313,515,535,616,10301,10501,11111,12521,13531,14141,
%T A117702 15151,15551,16361,20302,21512,22322,22522,23132,24542,25352
%N A117702 Palindromic primes in base 7 (written in base 7).
%H A117702 Harvey P. Dale, <a href="/A117702/b117702.txt">Table of n, a(n) for n = 1..1000</a>
%H A117702 Eric Weisstein: <a href="https://mathworld.wolfram.com/PalindromicPrime.html">Palindromic Prime</a>.
%t A117702 pal7Q[n_]:=Module[{idn7=IntegerDigits[n,7]},idn7==Reverse[idn7]]; FromDigits[ IntegerDigits[#,7]]&/@Select[Prime[Range[1000]],pal7Q] (* _Harvey P. Dale_, Aug 21 2021 *)
%Y A117702 Cf. A029975.
%K A117702 nonn,base
%O A117702 1,1
%A A117702 _Martin Renner_, Apr 13 2006