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 A143431 #15 Jul 15 2025 13:36:16
%S A143431 1,-1,1,-1,-1,1,-1,1,1,-1,1,-1,-1,1,-1,1,1,-1,1,-1,-1,1,-1,1,1,-1,1,
%T A143431 -1,-1,1,-1,1,1,-1,1,-1,-1,1,-1,1,1,-1,1,-1,-1,1,-1,1,1,-1,1,-1,-1,1,
%U A143431 -1,1,1,-1,1,-1,-1,1,-1,1,1,-1,1,-1,-1,1,-1,1,1,-1,1,-1,-1,1,-1,1,1,-1,1,-1,-1,1,-1,1,1,-1,1,-1,-1,1,-1,1,1,-1,1,-1,-1,1
%N A143431 Periodic length 8 sequence [1, -1, 1, -1, -1, 1, -1, 1, ...].
%C A143431 Nonsimple continued fraction expansion of (1+sqrt 5)/2= A001622. - _R. J. Mathar_, Mar 08 2012
%F A143431 Euler transform of length 8 sequence [ -1, 1, 0, -2, 0, 0, 0, 1].
%F A143431 a(-1 - n) = a(n). a(n + 4) = - a(n).
%F A143431 G.f.: (1 - x) * (1 + x^2) / (1 + x^4).
%e A143431 1 - x + x^2 - x^3 - x^4 + x^5 - x^6 + x^7 + x^8 - x^9 + x^10 - x^11 + ...
%t A143431 LinearRecurrence[{0,0,0,-1},{1,-1,1,-1},120] (* or *) PadRight[{},120,{1,-1,1,-1,-1,1,-1,1}] (* _Harvey P. Dale_, Jul 15 2025 *)
%o A143431 (PARI) a(n) = (-1)^(n + n\4)
%Y A143431 Convolution inverse of A143432.
%K A143431 sign,easy
%O A143431 0,1
%A A143431 _Michael Somos_, Aug 14 2008