a(0) = 1, a(n) = (-1)^n*(2-2^(n-1)) for n>0.

Terms

a(0) =1a(1) =-1a(2) =0a(3) =2a(4) =-6a(5) =14a(6) =-30a(7) =62a(8) =-126a(9) =254a(10) =-510a(11) =1022a(12) =-2046a(13) =4094a(14) =-8190a(15) =16382a(16) =-32766a(17) =65534a(18) =-131070a(19) =262142a(20) =-524286a(21) =1048574a(22) =-2097150a(23) =4194302a(24) =-8388606a(25) =16777214a(26) =-33554430a(27) =67108862a(28) =-134217726a(29) =268435454