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 A054790 #9 Sep 24 2012 08:47:03
%S A054790 0,2,10,4,30,6,50,8,70,11,20,90,13,120,15,140,17,160,19,180,100,22,
%T A054790 210,24,230,26,250,28,270,31,40,290,33,320,35,340,37,360,39,380,300,
%U A054790 42,410,44,430,46,450,48,470,51,60,490,53,520,55,540,57,560,59,580,500,62,610
%N A054790 Earliest sequence with a(a(n))=10n.
%H A054790 <a href="/index/Aa#aan">Index entries for sequences of the a(a(n)) = 2n family</a>
%t A054790 a[0] = 0; a[n_] := Which[m = Mod[n, 20]; m == 0, 10*n-100, m == 9, n+2, m == 10, n+10, m == 11, 10*n-20, MemberQ[ {2, 4, 6, 8, 13, 15, 17, 19}, m], 10*n-10, True, n+1]; Table[ a[n], {n, 0, 62}] (* _Jean-François Alcover_, Sep 24 2012 *)
%Y A054790 Cf. A002516, A002517, A002518, A007379.
%K A054790 nice,nonn
%O A054790 0,2
%A A054790 _Henry Bottomley_, Apr 27 2000