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 A133456 #15 Dec 12 2023 08:53:18 %S A133456 3,3,-5,0,3,-1,-3,0,7,-3,-3,5,0,-3,1,3,0,-7,3,3,-5,0,3,-1,-3,0,7,-3, %T A133456 -3,5,0,-3,1,3,0,-7,3,3,-5,0,3,-1,-3,0,7,-3,-3,5,0,-3,1,3,0,-7 %N A133456 Period 18: repeat 3, 3, -5, 0, 3, -1, -3, 0, 7 followed by their negatives. %H A133456 <a href="/index/Rec#order_09">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,0,0,0,0,0,0,-1). %F A133456 First differences 1, 4, 7, 2, 2, 5, 4 = A133390. %F A133456 a(n) = -a(n-9) for n > 8. G.f.: (7*x^8 - 3*x^6 - x^5 + 3*x^4 - 5*x^2 + 3*x + 3)/(x^9 + 1). - _Chai Wah Wu_, Jun 04 2016 %o A133456 (PARI) a(n)=[3, 3, -5, 0, 3, -1, -3, 0, 7][n%9+1]*(-1)^(n\9) \\ _Charles R Greathouse IV_, Jul 13 2016 %K A133456 sign,easy %O A133456 0,1 %A A133456 _Paul Curtz_, Nov 27 2007