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 A307348 #46 Feb 16 2025 08:33:55 %S A307348 12,30,40 %N A307348 Numbers k such that there are no palindromic triangular numbers of length k. %H A307348 Patrick De Geest, <a href="https://www.worldofnumbers.com/nobase10pg2.htm">Palindromic Squares in bases 2 to 17</a> %H A307348 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/PalindromicNumber.html">Palindromic Number</a> %t A307348 A003098 = Select[PolygonalNumber[3, Range[0, 10^6]], PalindromeQ]; %t A307348 (* Set Range to level of desired running time. *) %t A307348 nopal[n_] := Length[Select[A003098, IntegerLength[#] == n || (n == 1 && # == 0) &]]; Select[Range[12], nopal[#] == 0 &] %t A307348 (* Set Range to encompass length of last value in A003098. *) %Y A307348 Cf. A000217, A003098, A008509, A034822. %K A307348 nonn,base,hard,more %O A307348 1,1 %A A307348 _Robert Price_, May 01 2019