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 A100026 #15 Apr 09 2025 21:05:56
%S A100026 0,3,3,3,5,8,323,5,8,212,3,161,8,3,242,3,8,10901,737,161,242,333,282,
%T A100026 6,252,474,5,12921,8,131,18381,6,444,6,797,606,717,15351,464,333,626,
%U A100026 545,13031,161,747,191,323,636,32523,303,282,888,686,18981,111,15951,12021
%N A100026 Consider all (2n+1)-digit palindromic primes of the form 10...0M0...01 (so that M is a palindrome with <= 2n-1 digits); a(n) = smallest such M.
%C A100026 Is this the same as "Longest palindromic proper substring of A100027(n) or A028989(n+1) that occurs only once in the decimal representation of A100027(n) or A028989(n+1), respectively"? - _Felix Fröhlich_, Apr 30 2022
%C A100026 A more formal definition may be a(n) = A004151(A028989(n+1) - 10^(2n) - 1) with the convention that A004151(0) = 0. Only in the unlikely situation that A080176 contains undiscovered primes will a(n) = 0 occur for n > 1. - _Jeppe Stig Nielsen_, Apr 04 2025
%H A100026 Chai Wah Wu, <a href="/A100026/b100026.txt">Table of n, a(n) for n = 1..1000</a>
%t A100026 f[n_] := Block[{k = 0, t = Flatten[Join[{1}, Table[0, {n - 1}]]]}, While[s = Drop[t, Min[ -Floor[ Log[10, k]/2], 0]]; k != FromDigits[ Reverse[ IntegerDigits[k]]] || !PrimeQ[ FromDigits[ Join[s, IntegerDigits[k], Reverse[s]]]], k++ ]; k]; Table[ f[n], {n, 56}] (* _Robert G. Wilson v_, Nov 22 2004 *)
%Y A100026 The corresponding palindromic primes are shown in A100027.
%Y A100026 Cf. A028989, A099744, A099746, A100028.
%K A100026 nonn,base
%O A100026 1,2
%A A100026 Harvey Dubner (harvey(AT)dubner.com), Nov 20 2004
%E A100026 More terms from _Robert G. Wilson v_, Nov 22 2004