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 A117445 #26 Jan 23 2025 23:30:23
%S A117445 0,-1,1,4,-1,4,-4,-4,1,1,-4,-4,4,-1,4,1,-1,0,-1,1,4,-1,4,-4,-4,1,1,-4,
%T A117445 -4,4,-1,4,1,-1,0,-1,1,4,-1,4,-4,-4,1,1,-4,-4,4,-1,4,1,-1,0,-1,1,4,-1,
%U A117445 4,-4,-4,1,1,-4,-4,4,-1,4,1,-1,0,-1,1,4,-1,4,-4,-4,1,1,-4,-4
%N A117445 Periodic {0,-1,1,4,-1,4,-4,-4,1,1,-4,-4,4,-1,4,1,-1} (period 17).
%H A117445 <a href="/index/Rec#order_16">Index entries for linear recurrences with constant coefficients</a>, signature (-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1).
%F A117445 G.f.: (-1)*x*(1+x)*(1-x)^2*(1 -3*x^2 -3*x^3 -10*x^4 -6*x^5 -9*x^6 -6*x^7 -10*x^8 -3*x^9 -3*x^10 +x^12)/(1-x^17).
%F A117445 a(n) = (1/2)*Sum_{k=0..17} L(k*(k^2-n)/17), where L(j/p) is the Legendre symbol of j and p.
%F A117445 G.f.: (-x)*(1-x)*(1+x)*(1 -3*x^2 -3*x^3 -10*x^4 -6*x^5 -9*x^6 -6*x^7 -10*x^8 -3*x^9 -3*x^10 +x^12)/(1 +x +x^2 +x^3 +x^4 +x^5 +x^6 +x^7 +x^8 +x^9 +x^10 +x^11 +x^12 +x^13 +x^14 +x^15 +x^16). - _R. J. Mathar_, Feb 23 2015
%t A117445 PadRight[{},60,{0,-1,1,4,-1,4,-4,-4,1,1,-4,-4,4,-1,4,1,-1}] (* _Harvey P. Dale_, Sep 11 2012 *)
%t A117445 LinearRecurrence[{-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1},{0,-1,1,4,-1,4,-4,-4,1,1,-4,-4,4,-1,4,1},80]
%t A117445 (* _Ray Chandler_, Jul 15 2015 *)
%Y A117445 Cf. A117444.
%K A117445 easy,sign
%O A117445 0,4
%A A117445 _Paul Barry_, Mar 16 2006