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 A247487 #20 Jun 14 2025 23:49:14
%S A247487 2,1,1,1,1,-1,-3,-7,-31,-17,-19,-23,-47,-1,29,89,449,271,333,457,1201,
%T A247487 287,-131,-967,-5983,-4049,-5459,-8279,-25199,-8641,-3363,7193,70529,
%U A247487 56143,83981,139657,473713,194399,137789,24569,-654751,-703889,-1205907,-2209943
%N A247487 Expansion of (2 + x + x^2 + x^3 - x^4 - 2*x^5 - 4*x^6 - 8*x^7) / (1 - x^4 + 16*x^8) in powers of x.
%H A247487 G. C. Greubel, <a href="/A247487/b247487.txt">Table of n, a(n) for n = 0..2500</a>
%H A247487 <a href="/index/Rec#order_08">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,0,1,0,0,0,-16).
%F A247487 a(n) = a(-n) * 2^n = a(n-4) - 16*a(n-8) for all n in Z.
%F A247487 a(2*n + 1) = (-1)^n * A087168(n).
%F A247487 A247518(n) = a(n+1) * a(n) * a(n-1) * a(n-2) for all n in Z.
%e A247487 G.f. = 2 + x + x^2 + x^3 + x^4 - x^5 - 3*x^6 - 7*x^7 - 31*x^8 - 17*x^9 + ...
%p A247487 seq(coeff(series((2+x+x^2+x^3-x^4-2*x^5-4*x^6-8*x^7)/(1-x^4+16*x^8), x,n+1),x,n),n=0..50); # _Muniru A Asiru_, Aug 05 2018
%t A247487 CoefficientList[Series[(2+x+x^2+x^3-x^4-2*x^5-4*x^6-8*x^7)/(1 -x^4 + 16*x^8), {x, 0, 60}], x] (* _G. C. Greubel_, Aug 05 2018 *)
%o A247487 (PARI) {a(n) = if( n<0, n=-n; 2^-n, 1) * polcoeff( (2 + x + x^2 + x^3 - x^4 - 2*x^5 - 4*x^6 - 8*x^7) / (1 - x^4 + 16*x^8) + x * O(x^n), n)};
%o A247487 (Magma) m:=60; R<x>:=PowerSeriesRing(Integers(), m); Coefficients(R!((2+x+x^2+x^3-x^4-2*x^5-4*x^6-8*x^7)/(1-x^4+16*x^8))); // _G. C. Greubel_, Aug 05 2018
%o A247487 (GAP) a:=[2,1,1,1,1,-1,-3,-7];; for n in [9..50] do a[n]:=a[n-4]-16*a[n-8]; od; a; # _Muniru A Asiru_, Aug 05 2018
%Y A247487 CF. A087168, A247518.
%K A247487 sign,easy
%O A247487 0,1
%A A247487 _Michael Somos_, Sep 18 2014