%I A128019
%S A128019 1,3,3,9,9,27,27,81,81,243,243,729,729,2187,2187,6561,6561,19683,19683,
%T A128019 59049,59049,177147,177147,531441,531441,1594323,1594323,4782969,
%U A128019 4782969,14348907,14348907,43046721
%V A128019 1,-3,-3,9,9,-27,-27,81,81,-243,-243,729,729,-2187,-2187,6561,6561,-19683,
               -19683,59049,
%W A128019 59049,-177147,-177147,531441,531441,-1594323,-1594323,4782969,4782969,
               -14348907,
%X A128019 -14348907,43046721
%N A128019 Expansion of (1-3x)/(1+3x^2).
%C A128019 Binomial transform is A128018.
%F A128019 a(n)=3^floor((n+1)/2)*(-1)^C(n+1,2);
%Y A128019 Cf. A108411.
%Y A128019 Sequence in context: A147510 A146474 A145957 this_sequence A108411 A056449 
               A162436
%Y A128019 Adjacent sequences: A128016 A128017 A128018 this_sequence A128020 A128021 
               A128022
%K A128019 easy,sign
%O A128019 0,2
%A A128019 Paul Barry (pbarry(AT)wit.ie), Feb 11 2007