a(n) = 2^floor(n/2)*((-1)^floor(n/2) + (-1)^n)/2.

Terms

a(0) =1a(1) =0a(2) =0a(3) =-2a(4) =4a(5) =0a(6) =0a(7) =-8a(8) =16a(9) =0a(10) =0a(11) =-32a(12) =64a(13) =0a(14) =0a(15) =-128a(16) =256a(17) =0a(18) =0a(19) =-512a(20) =1024a(21) =0a(22) =0a(23) =-2048a(24) =4096a(25) =0a(26) =0a(27) =-8192a(28) =16384a(29) =0