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 A084241 #18 May 09 2024 04:42:00
%S A084241 0,1,-5,21,-85,341,-1365,5461,-21845,87381,-349525,1398101,-5592405,
%T A084241 22369621,-89478485,357913941,-1431655765,5726623061,-22906492245,
%U A084241 91625968981,-366503875925,1466015503701,-5864062014805,23456248059221,-93824992236885
%N A084241 a(n) = -5*a(n-1)-4*a(n-2) with n>1, a(0)=0, a(1)=1.
%C A084241 Binomial transform is (0,1,-3,9,-27,...).
%H A084241 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (-5,-4).
%F A084241 a(n) = ((-1)^n-(-4)^n)/3.
%F A084241 a(n) = Sum_{k=1..n} (-1)^(n+k)*binomial(n, k)*(-3)^(k-1).
%F A084241 G.f.: x/((1+x)*(1+4*x)).
%F A084241 E.g.f.: (exp(-x)-exp(-4x))/3.
%F A084241 abs(a(n)) = A002450(n) = A001045(2n).
%t A084241 LinearRecurrence[{-5,-4},{0,1},40] (* _Harvey P. Dale_, Dec 20 2014 *)
%Y A084241 Apart from signs, identical to A002450.
%Y A084241 Cf. A084240.
%K A084241 sign,easy
%O A084241 0,3
%A A084241 _Paul Barry_, May 21 2003