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 A077847 #12 Jul 31 2015 12:07:22
%S A077847 1,3,9,23,59,147,367,911,2263,5615,13935,34575,85791,212863,528159,
%T A077847 1310463,3251519,8067647,20017407,49667071,123233663,305766655,
%U A077847 758666495,1882398975,4670597631,11588660223,28753717759,71343560703,177017236479,439214158847
%N A077847 Expansion of (1-x)^(-1)/(1-2*x-2*x^2+2*x^3).
%H A077847 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (3, 0, -4, 2).
%F A077847 a(n) = -1+2*A077937(n)-2*A077937(n-2). [From _R. J. Mathar_, Nov 10 2009]
%F A077847 a(0)=1, a(1)=3, a(2)=9, a(3)=23, a(n)=3*a(n-1)-4*a(n-3)+2*a(n-4). - _Harvey P. Dale_, Apr 02 2013
%t A077847 CoefficientList[Series[(1-x)^(-1)/(1-2x-2x^2+2x^3),{x,0,40}],x] (* or *) LinearRecurrence[{3,0,-4,2},{1,3,9,23},40] (* _Harvey P. Dale_, Apr 02 2013 *)
%o A077847 (PARI) Vec((1-x)^(-1)/(1-2*x-2*x^2+2*x^3)+O(x^99)) \\ _Charles R Greathouse IV_, Sep 26 2012
%Y A077847 Cf. A052987.
%K A077847 nonn,easy
%O A077847 0,2
%A A077847 _N. J. A. Sloane_, Nov 17 2002