%I A078126
%S A078126 1,1,0,1,3,5,8,11,15,19,24,29,35,41,48,55,63,71,80,89,99,109,120,131,
%T A078126 143,155,168,181,195,209,224,239,255,271,288,305,323,341,360,379,399,
%U A078126 419,440,461,483,505,528,551,575,599,624,649,675,701,728,755,783,811
%V A078126 -1,-1,0,1,3,5,8,11,15,19,24,29,35,41,48,55,63,71,80,89,99,109,120,131,
               143,155,168,
%W A078126 181,195,209,224,239,255,271,288,305,323,341,360,379,399,419,440,461,483,
               505,528,551,
%X A078126 575,599,624,649,675,701,728,755,783,811
%N A078126 Negative determinant of n X n matrix M_{i,j}=1 if i=j or i+j=1 (mod 2 
               ).
%C A078126 a(n) = A002620(n) - 1.
%F A078126 G.f.: (-1+x+2x^2-x^3)/((1-x^2)(1-x)^2).
%Y A078126 a(n)=A002623(n-2)-A002623(n-3)-1, n>=0. a(n)=A024026(n-1), n>1.
%Y A078126 Sequence in context: A001463 A145197 A024169 this_sequence A024206 A159325 
               A049706
%Y A078126 Adjacent sequences: A078123 A078124 A078125 this_sequence A078127 A078128 
               A078129
%K A078126 sign,easy,nice
%O A078126 0,5
%A A078126 Michael Somos, Nov 18 2002