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 A117775 #23 Feb 16 2025 08:33:00 %S A117775 1,1,3,3,6,6,18,18,26,26,73,73,179,179,459,459,1179,1179,3004,3004, %T A117775 8111,8111,22183,22183,60789,60789,168641,168641,469689,469689, %U A117775 1322664,1322664,3691761,3691761,10390938,10390938,29502559,29502559,84012658,84012658,239417332,239417332 %N A117775 Total number of palindromic primes in base 3 below 3^n. %C A117775 Every palindrome with an even number of digits is divisible by 11 (in base 3) and therefore is composite (not prime). Hence there is no palindromic prime with an even number of digits. %H A117775 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/PalindromicPrime.html">Palindromic Prime</a>. %F A117775 a(2*k-1) = a(2*k) for k >= 1. - _Bernard Schott_, Mar 23 2021 %e A117775 a(5) = a(6) = 6 as the six palindromic primes below 3^5 are 2_10 = 2_3, 13_10 = 111_3, 23_10 = 212_3, 151_10 = 12121_3, 173_10 = 20102_3, 233_10 = 22122_3. There are no palindromic primes with 6 digits so a(5) = a(6). - _David A. Corneth_, Mar 21 2021 %Y A117775 Partial sums of A117776. %Y A117775 Cf. A029971, A117698. %Y A117775 Cf. A117772, A117777, A117779, A117781, A117783, A117785, A117787. %K A117775 nonn,base %O A117775 1,3 %A A117775 _Martin Renner_, Apr 15 2006 %E A117775 a(15)-a(42) from the data at A117776 added by _Amiram Eldar_, Mar 21 2021