a(1)=2, a(2)=4, a(3)=6; a(n+3) = a(n+2)+ 2*a(n), n>=1.

Terms

a(0) =2a(1) =4a(2) =6a(3) =14a(4) =26a(5) =54a(6) =106a(7) =214a(8) =426a(9) =854a(10) =1706a(11) =3414a(12) =6826a(13) =13654a(14) =27306a(15) =54614a(16) =109226a(17) =218454a(18) =436906a(19) =873814a(20) =1747626a(21) =3495254a(22) =6990506a(23) =13981014a(24) =27962026a(25) =55924054a(26) =111848106a(27) =223696214a(28) =447392426a(29) =894784854