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 A120218 #12 Jun 28 2020 11:32:36 %S A120218 100103,301003,300105,501005,500107,701007,700109,901009,900111, %T A120218 111011,110113,311013,310115,511015,510117,711017,710119,911019, %U A120218 910121,121021,120123,321023,320125,521025,520127,721027,720129,921029,920131,131031 %N A120218 Start with 100103 and repeatedly reverse the digits and add 2 to get the next term. %C A120218 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(100103,2). 100103 is the first S for which T(S,2) reaches a cycle of length 900. The cycle is simply the first 900 terms, which then repeat. A full period is given in the table. %H A120218 Klaus Brockhaus, <a href="/A120218/b120218.txt">Table of n, a(n) for n = 1..900</a> %H A120218 N. J. A. Sloane and others, <a href="/wiki/Sequences_of_RADD_type">Sequences of RADD type</a>, OEIS wiki. %H A120218 <a href="/index/Rec#order_900">Index entries for linear recurrences with constant coefficients</a>, order 900. %t A120218 NestList[FromDigits[Reverse[IntegerDigits[#]]]+2&,100103,30] (* _Harvey P. Dale_, Aug 14 2012 *) %Y A120218 Cf. A117521, A118514, A120214, A120215, A120216, A120217. %K A120218 nonn,base %O A120218 1,1 %A A120218 _Klaus Brockhaus_, Jun 11 2006