If n is even then 2^n+1 otherwise 2^n.

Terms

a(0) =2a(1) =2a(2) =5a(3) =8a(4) =17a(5) =32a(6) =65a(7) =128a(8) =257a(9) =512a(10) =1025a(11) =2048a(12) =4097a(13) =8192a(14) =16385a(15) =32768a(16) =65537a(17) =131072a(18) =262145a(19) =524288a(20) =1048577a(21) =2097152a(22) =4194305a(23) =8388608a(24) =16777217a(25) =33554432a(26) =67108865a(27) =134217728a(28) =268435457a(29) =536870912