a(0) = 3, a(n+1) = 2*a(n) + periodic sequence of length 2: repeat [1, -2].

Terms

a(0) =3a(1) =7a(2) =12a(3) =25a(4) =48a(5) =97a(6) =192a(7) =385a(8) =768a(9) =1537a(10) =3072a(11) =6145a(12) =12288a(13) =24577a(14) =49152a(15) =98305a(16) =196608a(17) =393217a(18) =786432a(19) =1572865a(20) =3145728a(21) =6291457a(22) =12582912a(23) =25165825a(24) =50331648a(25) =100663297a(26) =201326592a(27) =402653185a(28) =805306368a(29) =1610612737