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 A309231 #15 Feb 06 2023 10:04:52
%S A309231 7,17,25,34,43,53,61,71,79,89,97,106,115,125,133,142,151,161,169,178,
%T A309231 187,197,205,215,223,233,241,250,259,269,277,287,295,305,313,322,331,
%U A309231 341,349,359,367,377,385,394,403,413,421,430,439,449,457,466,475,485
%N A309231 Column 3 of the array at A326662 see Comments.
%C A309231 This is the sequence (c(n)) defined by the complementary equation c(n) = a(2n) + b(2n), with initial value a(1) = 1. See A326662. Conjecture: 9n-c(n) is in {1,2} for all n.
%H A309231 Clark Kimberling, <a href="/A309231/b309231.txt">Table of n, a(n) for n = 1..10000</a>
%t A309231 mex[list_, start_] := (NestWhile[# + 1 &, start, MemberQ[list, #] &]);
%t A309231 a = b = c = {}; h = 2; k = 2;
%t A309231 Do[Do[AppendTo[a,
%t A309231 mex[Flatten[{a, b, c}], Max[Last[a /. {} -> {0}], 1]]];
%t A309231 AppendTo[b, mex[Flatten[{a, b, c}], Max[Last[b /. {} -> {0}], 1]]], {k}];
%t A309231 AppendTo[c, a[[h Length[a]/k]] + Last[b]], {150}]; c
%t A309231 (* _Peter J. C. Moses_, Jul 04 2019 *)
%Y A309231 Cf. A326662.
%K A309231 nonn,easy
%O A309231 1,1
%A A309231 _Clark Kimberling_, Jul 16 2019