a(n) = Pell(n+3) - Jacobsthal(n+4).

Terms

a(0) =0a(1) =1a(2) =8a(3) =27a(4) =84a(5) =237a(6) =644a(7) =1695a(8) =4376a(9) =11129a(10) =28000a(11) =69859a(12) =173180a(13) =427141a(14) =1049308a(15) =2569447a(16) =6275584a(17) =15295377a(18) =37215864a(19) =90426155a(20) =219466276a(21) =532154909a(22) =1289368500a(23) =3122076719a(24) =7555891560a(25) =18278599081a(26) =44202568208a(27) =106862692467