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 A074582 #11 Sep 08 2022 08:45:07
%S A074582 3,7,39,241,1499,9327,58035,361109,2246915,13980895,86992799,
%T A074582 541292033,3368061131,20956960551,130399710235,811381230021,
%U A074582 5048627019523,31413882696791,195465425009943,1216237188605169,7567747077883259
%N A074582 a(n) = S(3n), where S(n) is the generalized tribonacci sequence A001644.
%H A074582 G. C. Greubel, <a href="/A074582/b074582.txt">Table of n, a(n) for n = 0..1000</a>
%H A074582 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (7,-5,1).
%F A074582 a(n) = 7*a(n-1) - 5*a(n-2) + a(n-3), a(0)=3, a(1)=7, a(2)=39.
%F A074582 G.f.: (3-14*x+5*x^2)/(1-7*x+5*x^2-x^3).
%t A074582 CoefficientList[Series[(3-14*x+5*x^2)/(1-7*x+5*x^2-x^3), {x, 0, 30}], x]
%t A074582 LinearRecurrence[{7,-5,1},{3,7,39},30] (* _Harvey P. Dale_, Mar 24 2022 *)
%o A074582 (PARI) my(x='x+O('x^30)); Vec((3-14*x+5*x^2)/(1-7*x+5*x^2-x^3)) \\ _G. C. Greubel_, Apr 13 2019
%o A074582 (Magma) R<x>:=PowerSeriesRing(Integers(), 30); Coefficients(R!( (3-14*x+5*x^2)/(1-7*x+5*x^2-x^3) )); // _G. C. Greubel_, Apr 13 2019
%o A074582 (Sage) ((3-14*x+5*x^2)/(1-7*x+5*x^2-x^3)).series(x, 30).coefficients(x, sparse=False) # _G. C. Greubel_, Apr 13 2019
%Y A074582 Cf. A001644, A074581.
%K A074582 easy,nonn
%O A074582 0,1
%A A074582 Mario Catalani (mario.catalani(AT)unito.it), Aug 24 2002