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 A285013 #13 Oct 02 2019 12:06:38
%S A285013 1,1,2,2,5,5,13,15,41,52,144,203,578,877,2605,4140,12869,21147,69178,
%T A285013 115975,398766,678570,2450406,4213597,15939952,27644437,109304914,
%U A285013 190899322,787016238,1382958545,5931824093,10480142147,46673259309,82864869804,382473282504
%N A285013 Number of periodic palindromic structures of length n using an infinite alphabet.
%C A285013 See A285012 for additional information. Permuting the symbols will not change the structure.
%H A285013 Andrew Howroyd, <a href="/A285013/b285013.txt">Table of n, a(n) for n = 0..500</a>
%o A285013 (PARI) \\ Requires T from A285012.
%o A285013 seq(n)={my(A=T(n)); concat([1], vector(n, i, vecsum(A[i,])))} \\ _Andrew Howroyd_, Oct 02 2019
%Y A285013 Row sums of A285012.
%Y A285013 Cf. A165137, A284841, A285042.
%K A285013 nonn
%O A285013 0,3
%A A285013 _Andrew Howroyd_, Apr 07 2017
%E A285013 a(0)=1 prepended and terms a(28) and beyond from _Andrew Howroyd_, Oct 02 2019