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 A054789 #11 May 20 2021 14:37:48
%S A054789 0,2,9,4,27,6,45,8,63,18,11,90,13,108,15,126,17,144,81,20,171,22,189,
%T A054789 24,207,26,225,36,29,252,31,270,33,288,35,306,243,38,333,40,351,42,
%U A054789 369,44,387,54,47,414,49,432,51,450,53,468,405,56,495,58,513,60,531,62,549
%N A054789 Earliest sequence with a(a(n)) = 9n.
%H A054789 <a href="/index/Aa#aan">Index entries for sequences of the a(a(n)) = 2n family</a>
%t A054789 a[0] = 0; a[n_] := Which[m = Mod[n, 18]; m == 0, 9*n-81, m == 9, n+9, MemberQ[ {1, 3, 5, 7, 10, 12, 14, 16}, m], n+1, True, 9*n-9]; Table[ a[n], {n, 0, 62}] (* _Jean-François Alcover_, Sep 24 2012 *)
%Y A054789 Cf. A002516, A002517, A002518, A007379, A008585.
%K A054789 nice,nonn
%O A054789 0,2
%A A054789 _Henry Bottomley_, Apr 27 2000