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 A206543 #24 Oct 15 2017 19:01:39
%S A206543 1,3,5,7,9,9,7,5,3,1,1,3,5,7,9,9,7,5,3,1,1,3,5,7,9,9,7,5,3,1,1,3,5,7,
%T A206543 9,9,7,5,3,1,1,3,5,7,9,9,7,5,3,1,1,3,5,7,9,9,7,5,3,1,1
%N A206543 Period 10: repeat 1, 3, 5, 7, 9, 9, 7, 5, 3, 1.
%C A206543 For general Modd n (not to be confused with mod n) see a comment on A203571. The present sequence gives the residues Modd 11 for the positive odd numbers not divisible by 11, which are given in A204454.
%C A206543 The underlying period length 22 sequence with offset 0 is P_11, also called Modd11, periodic([0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 0, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1]).
%H A206543 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (2,-2,2,-2,1).
%F A206543 a(n) = A204454(n) (Modd 11) := Modd11(A204454(n)), with the periodic sequence Modd11 with period length 22 given in the comment section.
%F A206543 O.g.f.: x*(1+x^9+3*x*(1+x^7)+5*x^2*(1+x^5)+7*x^3*(1+x^3)+9*x^4*(1+x))/(1-x^10) = x*(1+x)*(1-x^5)/((1+x^5)*(1-x)^2).
%e A206543 Residue Modd 11 of the positive odd numbers not divisible by 11:
%e A206543 A204454: 1, 3, 5, 7, 9, 13, 15, 17, 19, 21, 23, 25, 27, ...
%e A206543 Modd 11: 1, 3, 5, 7, 9, 9, 7, 5, 3, 1, 1, 3, 5, ...
%t A206543 PadRight[{},120,{1,3,5,7,9,9,7,5,3,1}] (* or *) LinearRecurrence[{2,-2,2,-2,1},{1,3,5,7,9},120] (* _Harvey P. Dale_, Oct 15 2017 *)
%o A206543 (PARI) a(n)=[1, 3, 5, 7, 9, 9, 7, 5, 3, 1][n%10+1] \\ _Charles R Greathouse IV_, Jul 17 2016
%Y A206543 Cf. A000012 (Modd 3), A084101 (Modd 5), A110551 (Modd 7).
%K A206543 nonn,easy
%O A206543 1,2
%A A206543 _Wolfdieter Lang_, Feb 09 2012