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 A081628 #28 Dec 06 2023 08:33:59
%S A081628 1,3,-23,123,-623,3123,-15623,78123,-390623,1953123,-9765623,48828123,
%T A081628 -244140623,1220703123,-6103515623,30517578123,-152587890623,
%U A081628 762939453123,-3814697265623,19073486328123,-95367431640623,476837158203123,-2384185791015623,11920928955078123
%N A081628 a(n) = 2*(-1)^n - (-5)^n.
%C A081628 Inverse binomial transform of A081629.
%H A081628 Vincenzo Librandi, <a href="/A081628/b081628.txt">Table of n, a(n) for n = 0..1000</a>
%H A081628 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (-6,-5).
%F A081628 G.f.: (1+9*x)/((1+x)*(1+5*x)).
%F A081628 E.g.f.: 2*exp(-x) - exp(-5*x).
%F A081628 a(n) = A033999(n)*(2 - A000351(n)). - _Elmo R. Oliveira_, Dec 05 2023
%t A081628 CoefficientList[Series[(1 + 9 x) / ((1 + x) (1 + 5 x)), {x, 0, 40}], x] (* _Vincenzo Librandi_, Aug 09 2013 *)
%t A081628 LinearRecurrence[{-6,-5},{1,3},30] (* _Harvey P. Dale_, Jan 08 2021 *)
%o A081628 (Magma) [2*(-1)^n-(-5)^n: n in [0..25]]; // _Vincenzo Librandi_, Aug 09 2013
%Y A081628 Cf. A000351, A033999, A081629.
%K A081628 easy,sign
%O A081628 0,2
%A A081628 _Paul Barry_, Mar 26 2003