a(2n) = a(2n-1) + 3a(2n-2), a(2n+1) = 2a(2n) + 3a(2n-1).

Terms

a(0) =1a(1) =1a(2) =4a(3) =11a(4) =23a(5) =79a(6) =148a(7) =533a(8) =977a(9) =3553a(10) =6484a(11) =23627a(12) =43079a(13) =157039a(14) =286276a(15) =1043669a(16) =1902497a(17) =6936001a(18) =12643492a(19) =46094987a(20) =84025463a(21) =306335887a(22) =558412276a(23) =2035832213a(24) =3711069041a(25) =13529634721a(26) =24662841844a(27) =89914587851