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 A089119 #16 Jan 30 2021 04:12:10
%S A089119 4,5,6,13,14,15,16,17,18,19,20,21,22,23,24,31,32,33,40,41,42,43,44,45,
%T A089119 46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,
%U A089119 69,70,71,72,73,74,75,76,77,78,85,86,87,94,95,96,97,98,99,100,101,102
%N A089119 Complement of ((3*A005836) union (3*A005836 - 1) union (3*A005836 - 2)).
%C A089119 Numbers k such that the Motzkin number A001006(k) == 0 (mod 3).
%C A089119 The asymptotic density of this sequence is 1 (Burns, 2016). - _Amiram Eldar_, Jan 30 2021
%H A089119 Amiram Eldar, <a href="/A089119/b089119.txt">Table of n, a(n) for n = 1..10000</a>
%H A089119 Rob Burns, <a href="https://arxiv.org/abs/1611.04910">Asymptotic density of Motzkin numbers modulo small primes</a>, arXiv:1611.04910 [math.NT], 2016.
%t A089119 (* m = MotzkinNumber *) m[0] = 1; m[n_] := m[n] = m[n - 1] + Sum[m[k]*m[n - 2 - k], {k, 0, n - 2}]; Select[Range[0, 120], Mod[m[#], 3] == 0 &] (* _Jean-François Alcover_, Jul 10 2013 *)
%Y A089119 Cf. A001006, A005836.
%K A089119 nonn
%O A089119 1,1
%A A089119 _Emeric Deutsch_ and _Bruce E. Sagan_, Dec 05 2003
%E A089119 Offset corrected by _Amiram Eldar_, Jan 30 2021