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 A199264 #42 Jul 27 2021 04:54:30
%S A199264 9,8,7,6,5,4,3,2,1,0,1,2,3,4,5,6,7,8,9,8,7,6,5,4,3,2,1,0,1,2,3,4,5,6,
%T A199264 7,8,9,8,7,6,5,4,3,2,1,0,1,2,3,4,5,6,7,8,9,8,7,6,5,4,3,2,1,0,1,2,3,4,
%U A199264 5,6,7,8,9,8,7,6,5,4,3,2,1,0,1,2,3,4,5
%N A199264 Period 18: repeat (9,8,7,6,5,4,3,2,1,0,1,2,3,4,5,6,7,8).
%C A199264 'Valley and Peak' sequence.
%C A199264 The sequence contains only values less than 10.
%C A199264 abs(a(n)-a(n+1)) = 1.
%C A199264 This sequence is in A158289. - _Omar E. Pol_, Feb 02 2012
%H A199264 Arkadiusz Wesolowski, <a href="/A199264/b199264.txt">Table of n, a(n) for n = 0..10000</a>
%H A199264 <a href="/index/Rec#order_10">Index entries for linear recurrences with constant coefficients</a>, signature (1,0,0,0,0,0,0,0,-1,1).
%F A199264 a(n) = 9 - A158289(n).
%F A199264 G.f.: ( -9+x+x^2+x^3+x^4+x^5+x^6+x^7+x^8-8*x^9 ) / ( (x-1)*(1+x)*(x^2-x+1)*(x^6-x^3+1) ). - _R. J. Mathar_, Nov 05 2011
%F A199264 a(n) = A158289(n+9). - _Omar E. Pol_, Feb 02 2012
%F A199264 a(n) = abs((n mod 18) - 9). - _Alonso del Arte_, Jul 03 2012
%t A199264 Flatten[Table[{9, 8, 7, 6, 5, 4, 3, 2, 1, 0, 1, 2, 3, 4, 5, 6, 7, 8}, {5}]] (* _Arkadiusz Wesolowski_, Dec 03 2011 *)
%t A199264 (* For Mathematica 7.0+ *) ArrayPad[Range[0, 9], {9, 68}, "Reflected"] (* _Arkadiusz Wesolowski_, Feb 02 2011 *)
%t A199264 Table[Abs[Mod[n, 18] - 9], {n, 0, 81}] (* _Alonso del Arte_, Jul 03 2012 *)
%t A199264 PadRight[{},90,Join[Range[9,0,-1],Range[8]]] (* _Harvey P. Dale_, Apr 08 2013 *)
%o A199264 (PARI) a(n)=[9,8,7,6,5,4,3,2,1,0,1,2,3,4,5,6,7,8][n%18+1] \\ _Charles R Greathouse IV_, Jul 17 2016
%Y A199264 Cf. A158289.
%K A199264 easy,nonn
%O A199264 0,1
%A A199264 _Arkadiusz Wesolowski_, Nov 04 2011