a(n) = 3*a(n-1) + 4*a(n-2), a(0) = 0, a(1) = 1.

Terms

a(0) =0a(1) =1a(2) =3a(3) =13a(4) =51a(5) =205a(6) =819a(7) =3277a(8) =13107a(9) =52429a(10) =209715a(11) =838861a(12) =3355443a(13) =13421773a(14) =53687091a(15) =214748365a(16) =858993459a(17) =3435973837a(18) =13743895347a(19) =54975581389a(20) =219902325555a(21) =879609302221