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 A002250 #32 Sep 15 2024 20:24:48
%S A002250 -1,-2,-2,10,94,538,2638,12010,52414,222778,930478,3840010,15714334,
%T A002250 63920218,258869518,1045044010,4208873854,16921588858,67944635758,
%U A002250 272553384010,1092538058974,4377125804698,17529423925198,70180457820010,280910117637694,1124205329623738,4498515895713838
%N A002250 a(n) = 4^n - 2*3^n.
%H A002250 Vincenzo Librandi, <a href="/A002250/b002250.txt">Table of n, a(n) for n = 0..1000</a>
%H A002250 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (7,-12).
%F A002250 From _Bruno Berselli_, Jan 25 2011: (Start)
%F A002250 G.f.: -(1-5*x)/((1-3*x)*(1-4*x)).
%F A002250 a(n) = 7*a(n-1) - 12*a(n-2) for n > 1. (End)
%F A002250 From _Elmo R. Oliveira_, Sep 15 2024: (Start)
%F A002250 E.g.f.: exp(3*x)*(exp(x) - 2).
%F A002250 a(n) = A000302(n) - A008776(n). (End)
%t A002250 Table[4^n - 2 3^n, {n, 0, 30}] (* or *) CoefficientList[Series[-(1 - 5 x) / ((1 - 3 x) (1 - 4 x)), {x, 0, 40}], x] (* _Vincenzo Librandi_, Jun 20 2013 *)
%o A002250 (Magma) [4^n-2*3^n: n in [0..30]]; // _Vincenzo Librandi_, Jun 20 2013
%o A002250 (PARI) a(n)=4^n-2*3^n \\ _Charles R Greathouse IV_, Jun 23 2020
%Y A002250 Cf. A000244, A000302, A005061, A008776.
%K A002250 sign,easy
%O A002250 0,2
%A A002250 _N. J. A. Sloane_