a(n) = 4*8^n + 1.

Terms

a(0) =5a(1) =33a(2) =257a(3) =2049a(4) =16385a(5) =131073a(6) =1048577a(7) =8388609a(8) =67108865a(9) =536870913a(10) =4294967297a(11) =34359738369a(12) =274877906945