a(n) = 3*a(n-1) + 4*a(n-2) - a(n-3) + 3*a(n-4) + 4*a(n-5).

Terms

a(0) =1a(1) =3a(2) =12a(3) =51a(4) =205a(5) =820a(6) =3277a(7) =13107a(8) =52428a(9) =209715a(10) =838861a(11) =3355444a(12) =13421773a(13) =53687091a(14) =214748364a(15) =858993459a(16) =3435973837a(17) =13743895348a(18) =54975581389a(19) =219902325555a(20) =879609302220