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 A117699 #6 Feb 16 2025 08:33:00 %S A117699 2,3,11,101,131,323,10001,11311,12121,13031,13331,30103,31013,31313, %T A117699 32023,33133,1003001,1013101,1101011,1120211,1123211,1133311,1201021, %U A117699 1212121,1221221,1302031,1311131,1321231 %N A117699 Palindromic primes in base 4 (written in base 4). %H A117699 Eric Weisstein: <a href="https://mathworld.wolfram.com/PalindromicPrime.html">Palindromic Prime</a>. %Y A117699 Cf. A029972. %K A117699 nonn,base %O A117699 1,1 %A A117699 _Martin Renner_, Apr 13 2006