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 A120216 #12 Oct 07 2016 09:56:50 %S A120216 100013,310003,300015,510005,500017,710007,700019,910009,900021, %T A120216 120011,110023,320013,310025,520015,510027,720017,710029,920019, %U A120216 910031,130021,120033,330023,320035,530025,520037,730027,720039,930029,920041,140031 %N A120216 Start with 100013 and repeatedly reverse the digits and add 2 to get the next term. %C A120216 Let T(S,Q) be the sequence obtained by starting with S and repeatedly reversing the digits and adding Q to get the next term. This is T(100013,2). 100013 is the first S for which T(S,2) reaches a cycle of length 1890. The cycle is simply the first 1890 terms, which then repeat. A full period is given in the table. %H A120216 Klaus Brockhaus, <a href="/A120216/b120216.txt">Table of n, a(n) for n = 1..1890</a> %H A120216 N. J. A. Sloane and others, <a href="/wiki/Sequences_of_RADD_type">Sequences of RADD type</a>, OEIS wiki. %H A120216 <a href="/index/Rec#order_1890">Index entries for linear recurrences with constant coefficients</a>, order 1890. %t A120216 NestList[FromDigits[Reverse[IntegerDigits[#]]]+2&,100013,30] (* _Harvey P. Dale_, Oct 03 2014 *) %Y A120216 Cf. A117521, A118514, A120214, A120215, A120217, A120218. %K A120216 nonn,base %O A120216 1,1 %A A120216 _Klaus Brockhaus_, Jun 11 2006