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 A026218 #14 Oct 17 2019 12:13:05
%S A026218 1,2,4,6,3,8,10,12,5,14,16,18,7,20,22,24,9,26,28,30,11,32,34,36,13,38,
%T A026218 40,42,15,44,46,48,17,50,52,54,19,56,58,60,21,62,64,66,23,68,70,72,25,
%U A026218 74,76,78,27,80,82,84,29,86,88,90,31,92,94
%N A026218 a(n) = (1/3)*(s(n) + 2), where s(n) is the n-th number congruent to 1 mod 3 in A026177.
%C A026218 This seems to be the same as A026200. - _Colin Barker_, Oct 15 2019
%o A026218 (PARI) \\ here S is A026177 as vector.
%o A026218 S(n)={my(a=vector(n)); a[1]=1; for(i=2, 2*n, my(h=i\2); if(i%2==0&&!a[i-h], a[i-h]=i, if(i+h<=n, a[i+h]=i))); a}
%o A026218 {[(k + 2)/3 | k<-S(500), k%3==1]} \\ _Andrew Howroyd_, Oct 15 2019
%Y A026218 Cf. A026177, A026200.
%K A026218 nonn,easy
%O A026218 1,2
%A A026218 _Clark Kimberling_