%I A128214
%S A128214 1,0,0,2,3,0,5,6,0,8,9,0,11,12,0,14,15,0,17,18,0,20,21,0,23,24,0,26,27,
%T A128214 0,29,30,0,32,33,0,35,36,0,38,39,0,41,42,0,44,45,0,47,48,0,50,51,0,53,
%U A128214 54
%V A128214 1,0,0,-2,3,0,-5,6,0,-8,9,0,-11,12,0,-14,15,0,-17,18,0,-20,21,0,-23,24,
               0,-26,27,0,-29,
%W A128214 30,0,-32,33,0,-35,36,0,-38,39,0,-41,42,0,-44,45,0,-47,48,0,-50,51,0,-53,
               54
%N A128214 Expansion of (1+2x+3x^2)/(1+x+x^2)^2.
%C A128214 Binomial transform is A128213.
%F A128214 a(n)=(1-n)cos(2*pi*n/3)+(n-1)*sin(2*pi*n/3)/sqrt(3)
%Y A128214 Sequence in context: A167485 A140508 A063956 this_sequence A145105 A140700 
               A055615
%Y A128214 Adjacent sequences: A128211 A128212 A128213 this_sequence A128215 A128216 
               A128217
%K A128214 easy,sign
%O A128214 0,4
%A A128214 Paul Barry (pbarry(AT)wit.ie), Feb 19 2007