a(0)=1, a(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