a(n) = 8/3 - 5*(-2)^n/3.

Terms

a(0) =1a(1) =6a(2) =-4a(3) =16a(4) =-24a(5) =56a(6) =-104a(7) =216a(8) =-424a(9) =856a(10) =-1704a(11) =3416a(12) =-6824a(13) =13656a(14) =-27304a(15) =54616a(16) =-109224a(17) =218456a(18) =-436904a(19) =873816a(20) =-1747624a(21) =3495256a(22) =-6990504a(23) =13981016a(24) =-27962024a(25) =55924056a(26) =-111848104a(27) =223696216a(28) =-447392424a(29) =894784856