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 A121213 #20 Mar 31 2025 17:56:44
%S A121213 0,2,24,218,1776,13682,102024,745418,5374176,38400482,272709624,
%T A121213 1928498618,13597146576,95668307282,672119557224,4717043931818,
%U A121213 33080342678976,231867574534082,1624598900644824,11379821699045018
%N A121213 a(n) = 7^n - 5^n.
%H A121213 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (12,-35).
%F A121213 a(n) = 12*a(n-1) - 35*a(n-2) with a(0)=0, a(1)=2. - _Vincenzo Librandi_, Jul 21 2010
%F A121213 a(n) = 2*A081200(n). - _Reinhard Zumkeller_, Aug 01 2010
%F A121213 G.f.: 2*x/((5*x-1)*(7*x-1)). - _Colin Barker_, Nov 05 2012
%F A121213 E.g.f.: 2*exp(6*x)*sinh(x). - _Elmo R. Oliveira_, Mar 31 2025
%t A121213 Table[7^n-5^n,{n,0,20}] (* or *) LinearRecurrence[{12,-35},{0,2},20] (* _Harvey P. Dale_, Feb 10 2018 *)
%o A121213 (PARI) a(n)=7^n-5^n \\ _Charles R Greathouse IV_, Oct 07 2015
%Y A121213 Cf. A074616, A081200.
%K A121213 nonn,easy
%O A121213 0,2
%A A121213 _Mohammad K. Azarian_, Aug 19 2006