%I #21 Apr 23 2023 18:22:24
%S -1,-1,2,0,1,-3,4,-2,3,-5,6,-4,5,-7,8,-6,7,-9,10,-8,9,-11,12,-10,11,
%T -13,14,-12,13,-15,16,-14,15,-17,18,-16,17,-19,20,-18,19,-21,22,-20,
%U 21,-23,24,-22,23,-25,26,-24,25,-27,28,-26,27,-29,30,-28,29,-31
%N -1 before list of quadruples -2n-1, 2n+2, -2n, 2n+1.
%H <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (-1,0,0,1,1).
%F a(n) = (1+(2*n-1)*(-1)^n-4*(-1)^((2*n-1+(-1)^n)/4))/4. - _Luce ETIENNE_, Sep 04 2016
%t Join[{-1},Table[{-2n-1,2n+2,-2n,2n+1},{n,0,20}]]//Flatten (* _Harvey P. Dale_, Apr 19 2023 *)
%K sign,easy
%O 0,3
%A _Paul Curtz_, Jan 31 2008