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 A190972 #44 Sep 08 2022 08:45:57
%S A190972 0,1,7,46,301,1969,12880,84253,551131,3605158,23582713,154263517,
%T A190972 1009096480,6600884809,43178904223,282449675134,1847611013269,
%U A190972 12085928067481,79058663432560,517152859825477,3382894028480659,22128799619888182,144752915253775297
%N A190972 a(n) = 7*a(n-1) - 3*a(n-2), with a(0)=0, a(1)=1.
%C A190972 a(n+1) equals the number of words of length n over {0,1,2,3,4,5,6} avoiding 01, 02 and 03. - _Milan Janjic_, Dec 17 2015
%H A190972 G. C. Greubel, <a href="/A190972/b190972.txt">Table of n, a(n) for n = 0..1000</a>
%H A190972 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (7,-3).
%F A190972 a(n) = ((7/2 + 1/2*sqrt(37))^n - (7/2 - 1/2*sqrt(37))^n)/sqrt(37). - _Giorgio Balzarotti_, May 28 2011
%F A190972 G.f.: x/(1 - 7x + 3*x^2). - _Philippe Deléham_, Oct 12 2011
%F A190972 E.g.f.: (2/sqrt(37))*exp(7*x/2)*sinh(sqrt(37)*x/2). - _G. C. Greubel_, Dec 18 2015
%t A190972 LinearRecurrence[{7,-3}, {0,1}, 50]
%o A190972 (Magma) I:=[0,1]; [n le 2 select I[n] else 7*Self(n-1)-3*Self(n-2): n in [1..30]]; // _Vincenzo Librandi_, Dec 17 2015
%o A190972 (PARI) concat(0, Vec(x/(1-7*x+3*x^2) + O(x^100))) \\ _Altug Alkan_, Dec 18 2015
%Y A190972 Cf. A190958 (index to generalized Fibonacci sequences).
%K A190972 nonn,easy
%O A190972 0,3
%A A190972 _Vladimir Joseph Stephan Orlovsky_, May 24 2011