%I #19 Dec 21 2019 15:51:41
%S 1,4,28,196,1372,9604,67228,470596,3294172,23059204,161414428,
%T 1129900996,7909306972,55365148804,387556041628,2712892291396,
%U 18990246039772,132931722278404,930522055948828,6513654391641796,45595580741492572,319169065190448004
%N Expansion of (1-3*x)/(1-7*x).
%C After 1, is this A208704?
%H Colin Barker, <a href="/A270471/b270471.txt">Table of n, a(n) for n = 0..1000</a>
%H <a href="/index/Rec#order_01">Index entries for linear recurrences with constant coefficients</a>, signature (7).
%F G.f.: (1-3*x)/(1-7*x).
%F a(n) = 7*a(n-1) for n>1.
%F a(n) = 4*7^(n-1) for n>0.
%t CoefficientList[Series[(1 - 3 x)/(1 - 7 x), {x, 0, 21}], x] (* _Michael De Vlieger_, Mar 18 2016 *)
%t Join[{1},NestList[7#&,4,20]] (* _Harvey P. Dale_, Dec 21 2019 *)
%o (PARI) Vec((1-3*x)/(1-7*x) + O(x^30))
%Y Cf. A208704.
%Y Cf. A000420 (powers of 7), A083076 (partial sums).
%Y Cf. A193577: (1-2*x)/(1-7*x); A169634: (1-4*x)/(1-7*x).
%K nonn,easy
%O 0,2
%A _Colin Barker_, Mar 17 2016