a(2*n) = 2*(2*4^(n-1)-1) and a(2*n-1) = 2*4^(n-1)-1.

Terms

a(0) =-1a(1) =1a(2) =2a(3) =7a(4) =14a(5) =31a(6) =62a(7) =127a(8) =254a(9) =511a(10) =1022a(11) =2047a(12) =4094a(13) =8191a(14) =16382a(15) =32767a(16) =65534a(17) =131071a(18) =262142a(19) =524287a(20) =1048574a(21) =2097151a(22) =4194302a(23) =8388607a(24) =16777214a(25) =33554431a(26) =67108862a(27) =134217727a(28) =268435454a(29) =536870911