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 A027720 #16 Aug 11 2024 14:41:29
%S A027720 1,2,5,101,626,10001,1000001,1040401,2217122,5053505,100000001,
%T A027720 101808101,10000000001,10182828101,10408080401,28053235082,
%U A027720 1000000000001,1000400040001,1018262628101,7534662664357,100000000000001,100018000810001,101826464628101
%N A027720 Palindromes of form k^2 + 1.
%C A027720 10^(2*m) + 1 for m >= 0 are terms. - _Chai Wah Wu_, May 25 2017
%H A027720 Giovanni Resta, <a href="/A027720/b027720.txt">Table of n, a(n) for n = 1..48</a>
%H A027720 P. De Geest, <a href="https://www.worldofnumbers.com/squadd1.htm">Palindromic incremented squares of the form n^2+1</a>
%F A027720 a(n) = A027719(n)^2 + 1. - _Giovanni Resta_, Aug 29 2018
%t A027720 palQ[n_] := Block[{d = IntegerDigits[n]}, d == Reverse[d]]; Select[Range[0, 10^5]^2 + 1, palQ] (* _Giovanni Resta_, Aug 29 2018 *)
%Y A027720 Cf. A002522, A027719, A070254, A002779.
%K A027720 nonn,base
%O A027720 1,2
%A A027720 _Patrick De Geest_
%E A027720 More terms from _Giovanni Resta_, Aug 28 2018