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 A190541 #30 Jun 07 2025 08:54:53
%S A190541 0,4,40,316,2320,16564,116920,821356,5758240,40333924,282416200,
%T A190541 1977149596,13840755760,96887416084,678218289880,4747547161036,
%U A190541 33232887522880,232630384847044,1628413210489960,11398894023111676,79792262810827600,558545853622930804,3909821017201928440
%N A190541 a(n) = 7^n - 3^n.
%C A190541 Length-n words from letters {1,2,...,7} with at least one letter greater than 3. - _Joerg Arndt_, Jun 02 2011
%H A190541 Vincenzo Librandi, <a href="/A190541/b190541.txt">Table of n, a(n) for n = 0..300</a>
%H A190541 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (10,-21).
%F A190541 a(n) = 10*a(n-1) - 21*a(n-2).
%F A190541 G.f.: 4*x/((1-3*x)*(1-7*x)). - _Vincenzo Librandi_, Oct 04 2014
%F A190541 a(n) = A000420(n) - A000244(n). - _Wesley Ivan Hurt_, Oct 04 2014
%F A190541 E.g.f.: 2*exp(5*x)*sinh(2*x). - _Elmo R. Oliveira_, Mar 31 2025
%F A190541 a(n) = 4*A016138(n-1). - _R. J. Mathar_, Jun 07 2025
%p A190541 A190541:=n->7^n-3^n: seq(A190541(n), n=0..25); # _Wesley Ivan Hurt_, Oct 04 2014
%t A190541 Table[7^n - 3^n, {n, 0, 25}] (* or *) CoefficientList[Series[4 x /((1 - 3 x) (1 - 7 x)), {x, 0, 30}], x] (* _Vincenzo Librandi_, Oct 04 2014 *)
%t A190541 LinearRecurrence[{10,-21},{0,4},20] (* _Harvey P. Dale_, Mar 30 2015 *)
%o A190541 (Magma) [7^n - 3^n: n in [0..30]];
%o A190541 (PARI) a(n)=7^n-3^n \\ _Charles R Greathouse IV_, Jun 02 2011
%Y A190541 Cf. A000244, A000420.
%Y A190541 Similar sequences: A121213, A016169.
%K A190541 nonn,easy
%O A190541 0,2
%A A190541 _Vincenzo Librandi_, Jun 02 2011