Expansion of g.f. (x + x^2)/(1 + 3*x^2).

Terms

a(0) =0a(1) =1a(2) =1a(3) =-3a(4) =-3a(5) =9a(6) =9a(7) =-27a(8) =-27a(9) =81a(10) =81a(11) =-243a(12) =-243a(13) =729a(14) =729a(15) =-2187a(16) =-2187a(17) =6561a(18) =6561a(19) =-19683a(20) =-19683a(21) =59049a(22) =59049a(23) =-177147a(24) =-177147a(25) =531441a(26) =531441a(27) =-1594323a(28) =-1594323a(29) =4782969