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 A181761 #17 Nov 10 2016 10:02:12
%S A181761 18,9,27,9,36,9,45,9,54,9,63,9,72,9,81,9,90,9,99,18,117,9,126,9,135,9,
%T A181761 144,9,153,9,162,9,171,9,180,9,189,18,207,9,216,9,225,9,234,9,243,9,
%U A181761 252,9,261,9,270,9,279,18,297,18,315,9,324,9,333,9,342,9
%N A181761 Start with 18; write down the sum of its digits; add last two terms; repeat.
%H A181761 Harvey P. Dale, <a href="/A181761/b181761.txt">Table of n, a(n) for n = 1..1000</a>
%F A181761 a(2n+1) = A016096(n+2). - _Michel Marcus_, Oct 31 2014
%e A181761 a(1)=18; a(2)=1+8=9; a(3)=18+9=27, etc.
%t A181761 NestList[{Total[#],Total[IntegerDigits[Total[#]]]}&,{18,9},40]// Flatten (* _Harvey P. Dale_, Nov 10 2016 *)
%Y A181761 Cf. A129888.
%K A181761 nonn,base
%O A181761 1,1
%A A181761 _Anton Joha_, Nov 14 2010