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 A156550 #16 Jan 31 2021 22:31:15
%S A156550 5,0,10,-10,30,-50,110,-210,430,-850,1710,-3410,6830,-13650,27310,
%T A156550 -54610,109230,-218450,436910,-873810,1747630,-3495250,6990510,
%U A156550 -13981010,27962030,-55924050,111848110,-223696210,447392430,-894784850,1789569710,-3579139410
%N A156550 a(n) = 5*(-1)^n*A078008(n).
%H A156550 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (-1,2).
%F A156550 a(n) = A140966(n)+A140966(n+2).
%F A156550 a(n) = 3*A140966(n)-A140966(n+1).
%F A156550 a(n+1) = 10*(-1)^n*A001045(n).
%F A156550 G.f.: 5*(1+x)/(1+x-2*x^2). - _R. J. Mathar_, Feb 23 2009
%F A156550 a(n) = (5*(2+(-2)^n))/3. - _Colin Barker_, Jun 10 2012
%F A156550 a(n) = -a(n-1) + 2*a(n-2) for n > 1. - _Klaus Purath_, Jan 30 2021
%F A156550 E.g.f.: 5*exp(-2*x)*(1 + 2*exp(3*x))/3. - _Stefano Spezia_, Jan 30 2021
%t A156550 LinearRecurrence[{-1, 2}, {5, 0}, 32] (* _Robert P. P. McKone_, Jan 31 2021 *)
%Y A156550 Cf. A001045, A078008, A140966.
%K A156550 sign,easy,less
%O A156550 0,1
%A A156550 _Paul Curtz_, Feb 09 2009
%E A156550 Edited and extended by _R. J. Mathar_ Feb 23 2009