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 A158678 #13 Dec 12 2023 08:09:20 %S A158678 0,0,0,3,0,0,0,3,0,-3,0,3,0,-3,0,0,0,-3,0,0,0,3,0,0,0,3,0,-3,0,3,0,-3, %T A158678 0,0,0,-3,0,0,0,3,0,0,0,3,0,-3,0,3,0,-3,0,0,0,-3 %N A158678 Period 18: repeat 0,0,0,3,0,0,0,3,0,-3,0,3,0,-3,0,0,0,-3. %H A158678 <a href="/index/Rec#order_12">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,0,0,0,-1,0,0,0,0,0,-1). %F A158678 a(n) = A158674(n) - A158677(n) = a(n-18). %F A158678 G.f.: 3*(1+x+x^2)*(x^2-x+1)*(x^4-x^2+1)*x^4/((x^6-x^3+1)*(x^6+x^3+1)). - _R. J. Mathar_, Apr 08 2009 %F A158678 a(n) = - a(n-6) - a(n-12) for n > 12. - _Chai Wah Wu_, Feb 18 2021 %Y A158678 Cf. A158674, A158677. %K A158678 sign,easy %O A158678 1,4 %A A158678 _Paul Curtz_, Mar 24 2009 %E A158678 Edited by _R. J. Mathar_, Apr 08 2009