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 A200561 #20 Feb 14 2018 03:16:24 %S A200561 2,-2,6,6,-10,70,-42,102,374,-506,2070,-90,182,16198,-16554,50406, %T A200561 46070,-77690,573078,-359898,884534,2980294,-4090410,17127270, %U A200561 -1465738,2996998,131089686,-136821594,422976950,352097350,-600716202,4688726502,-3073380106,7645103494,23717948310,-33014782170,141611506742 %N A200561 Expansion of -2*x / ( (2*x-1)*(4*x^2+3*x+1) ). %H A200561 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (-1,2,8). %F A200561 a(n) = -a(n-1) +2*a(n-2) +8*a(n-3). %F A200561 7*a(n) = 2^(n+1) -2*(-1)^n*(2*A049072(n-1)+A049072(n)). - _R. J. Mathar_, Dec 01 2011 %K A200561 sign,easy %O A200561 1,1 %A A200561 _Krishnamurthy Balasubraniam_, Nov 19 2011 %E A200561 Definition from _R. J. Mathar_, Nov 19 2011