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 A180853 #43 Dec 12 2023 07:41:00
%S A180853 4,6,9,7,5,4,6,9,7,5,4,6,9,7,5,4,6,9,7,5,4,6,9,7,5,4,6,9,7,5,4,6,9,7,
%T A180853 5,4,6,9,7,5,4,6,9,7,5,4,6,9,7,5,4,6,9,7,5,4,6,9,7,5,4,6,9,7,5,4,6,9,
%U A180853 7,5,4,6,9,7,5,4,6,9,7,5,4,6,9,7,5,4,6,9,7,5,4,6,9,7,5,4,6,9,7,5,4,6,9,7,5
%N A180853 Trajectory of 4 under map n->A006368(n).
%C A180853 The trajectory of 8 is a famous unsolved problem - see A028393.
%D A180853 D. Gale, Tracking the Automatic Ant and Other Mathematical Explorations, A Collection of Mathematical Entertainments Columns from The Mathematical Intelligencer, Springer, 1998; see p. 16.
%H A180853 J. H. Conway, <a href="http://www.jstor.org/stable/10.4169/amer.math.monthly.120.03.192">On unsettleable arithmetical problems</a>, Amer. Math. Monthly, 120 (2013), 192-198.
%H A180853 <a href="/index/3#3x1">Index entries for sequences related to 3x+1 (or Collatz) problem</a>
%H A180853 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,0,0,1)
%F A180853 Periodic with period of length 5.
%F A180853 G.f.: ( -4-6*x-9*x^2-7*x^3-5*x^4 ) / ( (x-1)*(1+x+x^2+x^3+x^4) ). - _R. J. Mathar_, Mar 10 2011
%F A180853 a(n+1) = A006368(a(n)).
%F A180853 a(n) = a(n-5). - _Wesley Ivan Hurt_, Apr 26 2021
%t A180853 Table[{4, 6, 9, 7, 5}, {21}] // Flatten (* _Jean-François Alcover_, Jun 10 2013 *)
%t A180853 PadRight[{},120,{4,6,9,7,5}] (* _Harvey P. Dale_, Jul 11 2020 *)
%o A180853 (Haskell)
%o A180853 a180853 n = a180853_list !! n
%o A180853 a180853_list = iterate a006368 4 -- _Reinhard Zumkeller_, Apr 18 2012
%o A180853 (PARI) Vec((-4-6*x-9*x^2-7*x^3-5*x^4)/((x-1)*(1+x+x^2+x^3+x^4))+O(x^99)) \\ _Charles R Greathouse IV_, Jun 12 2015
%Y A180853 Cf. A028397; A028398(3) = 4.
%Y A180853 Trajectories under A006368 and A006369: A180853, A217218, A185590, A180864, A028393, A028394, A094328, A094329, A028396, A028395, A217729, A182205, A223083-A223088, A185589.
%K A180853 nonn,easy
%O A180853 0,1
%A A180853 _N. J. A. Sloane_, Jan 22 2011