a(n) = 2^(n+3) - 6*n - 7.

Terms

a(0) =1a(1) =3a(2) =13a(3) =39a(4) =97a(5) =219a(6) =469a(7) =975a(8) =1993a(9) =4035a(10) =8125a(11) =16311a(12) =32689a(13) =65451a(14) =130981a(15) =262047a(16) =524185a(17) =1048467a(18) =2097037a(19) =4194183a(20) =8388481a(21) =16777083a(22) =33554293a(23) =67108719a(24) =134217577a(25) =268435299a(26) =536870749a(27) =1073741655a(28) =2147483473a(29) =4294967115