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 A266509 #20 Feb 14 2017 15:16:19
%S A266509 0,0,1,1,1,1,3,3,1,1,3,3,5,5,7,7,1,1,3,3,5,5,7,7,5,5,11,11,17,17,15,
%T A266509 15,1,1,3,3,5,5,7,7,5,5,11,11,17,17,15,15,5,5,11,11,17,17,23,23,29,29,
%U A266509 35,35,41,41,31,31,1,1,3,3,5,5,7,7,5,5,11,11,17,17,15,15,5,5,11,11,17,17,23,23,29,29
%N A266509 Terms of A256263 repeated.
%C A266509 First differs from A266529 at a(55), with which it shares infinitely many terms.
%C A266509 First differs from A266539 at a(25), with which it shares infinitely many terms.
%C A266509 For an illustration of initial terms consider the diagram of A256263 in the fourth quadrant of the square grid together with a reflected copy in the second quadrant.
%H A266509 Ivan Neretin, <a href="/A266509/b266509.txt">Table of n, a(n) for n = 1..8192</a>
%e A266509 Written as an irregular triangle in which the row lengths are twice the terms of A011782 the sequence begins:
%e A266509 0,0;
%e A266509 1,1;
%e A266509 1,1,3,3;
%e A266509 1,1,3,3,5,5,7,7;
%e A266509 1,1,3,3,5,5,7,7,5,5,11,11,17,17,15,15;
%e A266509 1,1,3,3,5,5,7,7,5,5,11,11,17,17,15,15,5,5,11,11,17,17,23,23,29,29,35,35,41,41,31,31;
%e A266509 ...
%e A266509 Row sums give 0 together with A004171.
%t A266509 Riffle[#, #] &@ Flatten@Join[{0}, NestList[Join[#, Range[Length[#] - 1]*6 - 1, {2 #[[-1]] + 1}] &, {1}, 5]] (* _Ivan Neretin_, Feb 14 2017 *)
%Y A266509 Partial sums give A266510.
%Y A266509 Cf. A004171, A011782, A256263, A256264, A256265, A266529, A266539.
%K A266509 nonn,tabf
%O A266509 1,7
%A A266509 _Omar E. Pol_, Jan 02 2016