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 A010035 #26 May 28 2025 09:18:29
%S A010035 1,15,153,1431,13041,117855,1062153,9563751,86086881,774821295,
%T A010035 6973509753,62761942071,564858541521,5083730062335,45753580126953,
%U A010035 411782249840391,3706040334656961,33354363270192975,300189270206577753,2701703434183722711,24315330914627073201
%N A010035 a(n) = 2*3^(2*n)-3^n.
%H A010035 Delbert L. Johnson, <a href="/A010035/b010035.txt">Table of n, a(n) for n = 0..1047</a>
%H A010035 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (12,-27).
%F A010035 a(n) = 12*a(n-1)-27*a(n-2). G.f.: (3*x+1) / ((3*x-1)*(9*x-1)). - _Colin Barker_, Oct 01 2014
%p A010035 f := n->2*3^(2*n)-3^n;
%t A010035 A010035[n_] := (2*# - 1)*# & [3^n]; Array[A010035, 25, 0] (* or *)
%t A010035 LinearRecurrence[{12, -27}, {1, 15}, 25] (* _Paolo Xausa_, May 28 2025 *)
%o A010035 (PARI) a(n) = 2*3^(2*n)-3^n \\ _Michel Marcus_, Jun 08 2013
%K A010035 nonn,easy
%O A010035 0,2
%A A010035 Steve King (ITTTUCSON(AT)aol.com)
%E A010035 Revised by _N. J. A. Sloane_, Jun 10 2013, replacing incorrect definition with formula from _Michel Marcus_ which matches the terms.
%E A010035 More terms, and corrections to name, Maple and prog to agree with the offset, from _Colin Barker_, Oct 01 2014