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 A027721 #14 Aug 11 2024 14:41:29
%S A027721 6,8,606,656,818,83238,6177716,6505056,8343438,8681868,834545438,
%T A027721 21543634512,69872727896,83456565438,85425552458,8032131312308,
%U A027721 8255470745528,8345676765438,8716172716178,8766434346678,8915858585198,8973808083798,213296020692312
%N A027721 Palindromes of form k^2 + k + 6.
%C A027721 Palindromes h such that 4*h - 23 is a square. - _Bruno Berselli_, Aug 29 2018
%H A027721 Giovanni Resta, <a href="/A027721/b027721.txt">Table of n, a(n) for n = 1..34</a>
%H A027721 P. De Geest, <a href="https://www.worldofnumbers.com/quasimor.htm">Palindromic Quasi_Over_Squares of the form n^2+(n+X)</a>
%F A027721 a(n) = A027729(n)^2 + A027729(n) + 6. - _Giovanni Resta_, Aug 27 2018
%t A027721 palQ[n_] := Block[{d = IntegerDigits[n]}, d == Reverse[d]]; f[n_] := n^2 + n + 6; Select[f@ Range[0, 10^5], palQ] (* _Giovanni Resta_, Aug 29 2018 *)
%Y A027721 Cf. A027729, A027691, A027728, A027723.
%K A027721 nonn,base
%O A027721 1,1
%A A027721 _Patrick De Geest_
%E A027721 More terms from _Giovanni Resta_, Aug 27 2018