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 A080199 #12 Feb 13 2019 07:53:27 %S A080199 1,7,13,19,25,31,28,34,40,46,52,58,55,61,67,73,79,85,82,88,94,100,106, %T A080199 112,109,115,121,118,124,130,127,133,139,136,142,148,154,160,166,163, %U A080199 169,175,181,187,193,190,196,202,208,214,220,217,223,229 %N A080199 a(1)=1; for n>1, a(n)=a(n-1) - 3 if n is already in the sequence, a(n)=a(n-1) + 6 otherwise. %H A080199 B. Cloitre, N. J. A. Sloane and M. J. Vandermast, <a href="http://www.cs.uwaterloo.ca/journals/JIS/VOL6/Cloitre/cloitre2.html">Numerical analogues of Aronson's sequence</a>, J. Integer Seqs., Vol. 6 (2003), #03.2.2. %H A080199 B. Cloitre, N. J. A. Sloane and M. J. Vandermast, <a href="http://arXiv.org/abs/math.NT/0305308">Numerical analogues of Aronson's sequence</a> (math.NT/0305308) %F A080199 a(n) = 3*n*(1 + 1/log_3(n)) + o(n). %t A080199 a[1] = 1; %t A080199 a[n_] := a[n] = If[MemberQ[Array[a, n-1], n], a[n-1]-3, a[n-1]+6]; %t A080199 Array[a, 54] (* _Jean-François Alcover_, Feb 13 2019 *) %Y A080199 Cf. A080455-A080458, A080036, A080037. %K A080199 nonn %O A080199 1,2 %A A080199 _N. J. A. Sloane_, Mar 20 2003