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 A118004 #26 Feb 16 2025 08:33:00
%S A118004 0,5,65,665,6305,58025,527345,4766585,42981185,387158345,3485735825,
%T A118004 31376865305,282412759265,2541798719465,22876524019505,
%U A118004 205890058352825,1853015893884545,16677164519797385,150094566577522385,1350851442795085145,12157664359545301025,109418984733465848105,984770884591425188465
%N A118004 a(n) = 9^n - 4^n.
%H A118004 G. C. Greubel, <a href="/A118004/b118004.txt">Table of n, a(n) for n = 0..1000</a>
%H A118004 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/CantorSquareFractal.html">Cantor Square Fractal</a>
%H A118004 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (13,-36).
%F A118004 a(n) = 5*A016153(n).
%F A118004 a(n) = 13*a(n-1) - 36*a(n-2), n>=2. - _Vincenzo Librandi_, Mar 16 2011
%F A118004 G.f.: 5*x / ( (1-4*x)*(1-9*x) ). - _R. J. Mathar_, Mar 18 2011
%F A118004 From _G. C. Greubel_, Nov 11 2024: (Start)
%F A118004 a(n) = A001047(n)*A007689(n).
%F A118004 E.g.f.: 2*exp(13*x/2)*sinh(5*x/2). (End)
%t A118004 Table[9^n-4^n,{n,0,30}] (* or *) LinearRecurrence[{13,-36},{0,5},30] (* _Harvey P. Dale_, May 11 2017 *)
%o A118004 (PARI) a(n)=9^n-4^n \\ _Charles R Greathouse IV_, Oct 07 2015
%o A118004 (Magma) [9^n-4^n: n in [0..30]]; // _G. C. Greubel_, Nov 11 2024
%o A118004 (SageMath)
%o A118004 A118004=BinaryRecurrenceSequence(13,-36,0,5)
%o A118004 [A118004(n) for n in range(31)] # _G. C. Greubel_, Nov 11 2024
%Y A118004 Cf. A001047, A007689, A016153.
%K A118004 nonn,easy
%O A118004 0,2
%A A118004 _Eric W. Weisstein_, Apr 09 2006
%E A118004 More terms added by _G. C. Greubel_, Nov 11 2024