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 A074581 #20 Jan 10 2025 19:25:21
%S A074581 0,2,13,81,504,3136,19513,121415,755476,4700770,29249425,181997601,
%T A074581 1132436852,7046319384,43844049029,272809183135,1697490356184,
%U A074581 10562230626642,65720971788709,408933139743937,2544489349890656
%N A074581 a(n) = T(3n+1), where T(n) are tribonacci numbers A000073.
%C A074581 In general, the trisection of a third-order linear recurrence with signature (x,y,z) will result in a third-order recurrence with signature (x^3 + 3*x*y + 3*z, -3*x*y*z + y^3 - 3*z^2, z^3). - _Gary Detlefs_, May 29 2024
%H A074581 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (7,-5,1).
%F A074581 a(n) = 7*a(n-1) - 5*a(n-2) + a(n-3), a(0)=0, a(1)=2, a(2)=13.
%F A074581 G.f.: (2*x - x^2)/(1 - 7*x + 5*x^2 - x^3). [corrected by _Nguyen Tuan Anh_, Jan 10 2025]
%t A074581 CoefficientList[Series[(2*x-x^2)/(1-7*x+5*x^2-x^3), {x, 0, 40}], x]
%t A074581 LinearRecurrence[{7,-5,1},{0,2,13},30] (* _Harvey P. Dale_, Jul 22 2021 *)
%Y A074581 Cf. A000073.
%K A074581 easy,nonn
%O A074581 0,2
%A A074581 Mario Catalani (mario.catalani(AT)unito.it), Aug 24 2002
%E A074581 Definition corrected by _David Scambler_, Oct 18 2010