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 A117783 #10 Feb 16 2025 08:33:00 %S A117783 3,3,9,9,50,50,204,204,1135,1135,6086,6086,36018,36018,216932,216932, %T A117783 1306070,1306070,8129138,8129138,51773946,51773946,326701423,326701423 %N A117783 Total number of palindromic primes in base 7 below 7^n. %C A117783 Every palindrome with an even number of digits is divisible by 11 (in base 7) and therefore is composite (not prime). Hence there is no palindromic prime with an even number of digits. %H A117783 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/PalindromicPrime.html">Palindromic Prime</a>. %Y A117783 Partial sums of A117784. %Y A117783 Cf. A029975, A117702. %Y A117783 Cf. A117772, A117775, A117777, A117779, A117781, A117785, A117787. %K A117783 nonn,base,more %O A117783 1,1 %A A117783 _Martin Renner_, Apr 15 2006 %E A117783 a(9)-a(24) from the data at A117784 added by _Amiram Eldar_, Mar 21 2021