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 A206544 #15 Jul 17 2016 20:06:28
%S A206544 1,3,5,7,9,11,11,9,7,5,3,1,1,3,5,7,9,11,11,9,7,5,3,1,1,3,5,7,9,11,11,
%T A206544 9,7,5,3,1,1,3,5,7,9,11,11,9,7,5,3,1,1,3,5,7,9,11,11,9,7,5,3,1,1,3,5,
%U A206544 7,9,11,11,9,7,5,3,1
%N A206544 Period 12: repeat 1, 3, 5, 7, 9, 11, 11, 9, 7, 5, 3, 1.
%C A206544 For general Modd n (not to be confused with mod n) see a comment on A203571. The present sequence gives the residues Modd 13 of the positive odd numbers not divisible by 13, which are given in A204457.
%C A206544 The underlying periodic sequence with period length 26 is periodic([0,1,2,3,4,5,6,7,8,9,10,11,12,0,12,11,10,9,8,7,6,5,4,3,2,1]), called, with offset 0, P_13 or Modd13.
%H A206544 <a href="/index/Rec#order_07">Index entries for linear recurrences with constant coefficients</a>, signature (1, 0, 0, 0, 0, -1, 1).
%F A206544 a(n) = A204457(n) (Modd 13) := Modd13(A204457(n)), n>=1, with the period length 26 periodic sequence Modd13 given in the comment section.
%F A206544 O.g.f.: x*(1+x^11+3*x*(1+x^9)+5*x^2*(1+x^7)+7*x^3*(1+x^5)+9*x^4*(1+x^3)+11*x^5*(1+x))/(1-x^12) = x*(1-x^6)*(1+x)/((1+x^6)*(1-x)^2).
%e A206544 Residue Modd 13 of the positive odd numbers not divisible by 13:
%e A206544 A204457: 1, 3, 5, 7, 9, 11, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, ...
%e A206544 Modd 13: 1, 3, 5, 7, 9, 11, 11, 9, 7, 5, 3, 1, 1, 3, 5, 7, ...
%t A206544 LinearRecurrence[{1, 0, 0, 0, 0, -1, 1},{1, 3, 5, 7, 9, 11, 11},72] (* _Ray Chandler_, Aug 08 2015 *)
%o A206544 (PARI) a(n)=[1, 1, 3, 5, 7, 9, 11, 11, 9, 7, 5, 3][n%12+1] \\ _Charles R Greathouse IV_, Jul 17 2016
%Y A206544 Cf. A000012 (Modd 3), A084101 (Modd 5), A110551 (Modd 7), A206543 (Modd 11).
%K A206544 nonn,easy
%O A206544 1,2
%A A206544 _Wolfdieter Lang_, Feb 09 2012