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 A081630 #14 Sep 08 2022 08:45:09
%S A081630 1,5,-7,29,-79,245,-727,2189,-6559,19685,-59047,177149,-531439,
%T A081630 1594325,-4782967,14348909,-43046719,129140165,-387420487,1162261469,
%U A081630 -3486784399,10460353205,-31381059607,94143178829,-282429536479,847288609445,-2541865828327,7625597484989
%N A081630 2-(-3)^n.
%C A081630 Binomial transform of A081629. Inverse binomial transform of A081631.
%H A081630 Vincenzo Librandi, <a href="/A081630/b081630.txt">Table of n, a(n) for n = 0..1000</a>
%H A081630 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (-2,3).
%F A081630 G.f.: (1+7*x)/((1-x)*(1+3*x)).
%F A081630 E.g.f. 2*exp(x)-exp(-3*x)
%t A081630 LinearRecurrence[{-2, 3}, {1, 5}, 30] (* _Harvey P. Dale_, Mar 25 2013 *)
%t A081630 CoefficientList[Series[(1 + 7 x) / ((1 - x) (1 + 3 x)), {x, 0, 40}], x] (* _Vincenzo Librandi_, Aug 09 2013 *)
%o A081630 (Magma) [2-(-3)^n: n in [0..30]]; // _Vincenzo Librandi_ Aug 09 2013
%K A081630 easy,sign
%O A081630 0,2
%A A081630 _Paul Barry_, Mar 26 2003