a(n) = a(n-1) + 2*a(n-2) with n>1, a(0)=2, a(1)=7.

Terms

a(0) =2a(1) =7a(2) =11a(3) =25a(4) =47a(5) =97a(6) =191a(7) =385a(8) =767a(9) =1537a(10) =3071a(11) =6145a(12) =12287a(13) =24577a(14) =49151a(15) =98305a(16) =196607a(17) =393217a(18) =786431a(19) =1572865a(20) =3145727a(21) =6291457a(22) =12582911a(23) =25165825a(24) =50331647a(25) =100663297a(26) =201326591a(27) =402653185a(28) =805306367a(29) =1610612737