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 A220946 #10 Aug 01 2015 10:40:21
%S A220946 1,2,6,7,21,22,66,67,201,202,606,607,1821,1822,5466,5467,16401,16402,
%T A220946 49206,49207,147621,147622,442866,442867,1328601,1328602,3985806,
%U A220946 3985807,11957421,11957422,35872266,35872267,107616801,107616802,322850406,322850407
%N A220946 Expansion of (1+2*x+2*x^2-x^3)/((1-x)*(1+x)*(1-3x^2)).
%H A220946 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0, 4, 0, -3).
%F A220946 a(n) = a(n-1)+1 if n odd, a(n) = a(n-1)*3 if n even.
%F A220946 a(2n) = A134931(n), a(2n+1) = A060816(n+1).
%F A220946 a(n) = 4*a(n-2) - 3*a(n-4) with a(0)=1, a(1)=2, a(2)=6, a(3)=7.
%t A220946 LinearRecurrence[{0, 4, 0, -3}, {1, 2, 6, 7}, 40] (* _T. D. Noe_, Apr 17 2013 *)
%Y A220946 Cf. A060816, A134931.
%K A220946 nonn,easy
%O A220946 0,2
%A A220946 _Philippe Deléham_, Apr 14 2013