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 A165147 #14 Aug 05 2025 13:03:13
%S A165147 1,9,69,501,3561,25089,176109,1234221,8643921,60520569,423683349,
%T A165147 2965901541,20761665081,145332718449,1017332217789,7121335090461,
%U A165147 49849374331041,348945706410729,2442620203155429,17098342196928981
%N A165147 a(n) = (3*7^n-3^n)/2.
%C A165147 Partial sums are in A016138.
%C A165147 Binomial transform of A016129. Inverse binomial transform of A165148.
%H A165147 Vincenzo Librandi, <a href="/A165147/b165147.txt">Table of n, a(n) for n = 0..300</a>
%H A165147 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (10,-21).
%F A165147 a(n) = 10*a(n-1)-21*a(n-2) for n > 1; a(0) = 1, a(1) = 9.
%F A165147 G.f.: (1-x)/((1-3*x)*(1-7*x)).
%t A165147 LinearRecurrence[{10, -21}, {1, 9}, 25] (* _Paolo Xausa_, Apr 22 2024 *)
%t A165147 Table[(3*7^n-3^n)/2,{n,0,20}] (* _Harvey P. Dale_, Aug 05 2025 *)
%o A165147 (Magma) [ (3*7^n-3^n)/2: n in [0..19] ];
%Y A165147 Cf. A016138, A016129, A165148.
%K A165147 nonn,easy
%O A165147 0,2
%A A165147 _Klaus Brockhaus_, Sep 15 2009