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 A270472 #23 Mar 25 2025 20:19:05
%S A270472 1,7,63,567,5103,45927,413343,3720087,33480783,301327047,2711943423,
%T A270472 24407490807,219667417263,1977006755367,17793060798303,
%U A270472 160137547184727,1441237924662543,12971141321962887,116740271897665983,1050662447078993847,9455962023710944623,85103658213398501607
%N A270472 Expansion of g.f. (1-2*x)/(1-9*x).
%H A270472 Colin Barker, <a href="/A270472/b270472.txt">Table of n, a(n) for n = 0..1000</a>
%H A270472 <a href="/index/Rec#order_01">Index entries for linear recurrences with constant coefficients</a>, signature (9).
%F A270472 G.f.: (1-2*x)/(1-9*x).
%F A270472 a(n) = 9*a(n-1) for n>1.
%F A270472 a(n) = 7*9^(n-1) for n>0.
%F A270472 a(n) = A005032(2*n-2). - _R. J. Mathar_, Jan 28 2025
%F A270472 E.g.f.: (7*exp(9*x) + 2)/9. - _Elmo R. Oliveira_, Mar 25 2025
%t A270472 CoefficientList[Series[(1 - 2 x)/(1 - 9 x), {x, 0, 20}], x] (* _Michael De Vlieger_, Mar 18 2016 *)
%o A270472 (PARI) Vec((1-2*x)/(1-9*x) + O(x^30))
%Y A270472 Cf. A001019 (powers of 9), A005032, A187709 (partial sums).
%Y A270472 Cf. A055275: (1-x)/(1-9*x); A092810: (1-3*x)/(1-9*x).
%K A270472 nonn,easy
%O A270472 0,2
%A A270472 _Colin Barker_, Mar 17 2016