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 A131738 #15 Aug 28 2025 06:07:02
%S A131738 0,-2,3,-4,5,-6,7,-8,9,-10,11,-12,13,-14,15,-16,17,-18,19,-20,21,-22,
%T A131738 23,-24,25,-26,27,-28,29,-30,31,-32,33,-34,35,-36,37,-38,39,-40,41,
%U A131738 -42,43,-44,45,-46,47,-48,49,-50,51,-52,53,-54,55,-56,57,-58,59,-60,61,-62,63,-64,65,-66,67,-68,69,-70,71,-72,73,-74,75
%N A131738 a(0) = 0. a(n) = (n+1)*(-1)^n, n>0 .
%C A131738 Also the main diagonal of A138057.
%H A131738 G. C. Greubel, <a href="/A131738/b131738.txt">Table of n, a(n) for n = 0..5000</a>
%H A131738 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (-2,-1).
%F A131738 From _G. C. Greubel_, Nov 02 2017: (Start)
%F A131738 a(n) = -2*a(n-1) - a(n-2).
%F A131738 G.f.: -x*(x+2)/(1+x)^2.
%F A131738 E.g.f.: (1 - x - exp(x))*exp(-x). (End)
%t A131738 Join[{0}, Table[(-1)^n*(n + 1), {n, 1, 50}]] (* _G. C. Greubel_, Nov 02 2017 *)
%t A131738 LinearRecurrence[{-2,-1},{0,-2,3},80] (* _Harvey P. Dale_, Dec 03 2022 *)
%o A131738 (PARI) a(n)=if(n,(n+1)*(-1)^n,0) \\ _Charles R Greathouse IV_, Sep 01 2015
%o A131738 (Magma) [0] cat [(-1)^n*(n+1): n in [1..50]]; // _G. C. Greubel_, Nov 02 2017
%Y A131738 Cf. A105811.
%Y A131738 Cf. A181983 (main entry).
%K A131738 sign,easy,less,changed
%O A131738 0,2
%A A131738 _Paul Curtz_, Sep 19 2007
%E A131738 Edited by _R. J. Mathar_, Jul 07 2008