a(n) = a(n-1)+9*a(n-2) initialized with a(0)=1, a(1)=3.

Terms

a(0) =1a(1) =3a(2) =12a(3) =39a(4) =147a(5) =498a(6) =1821a(7) =6303a(8) =22692a(9) =79419a(10) =283647a(11) =998418a(12) =3551241a(13) =12537003a(14) =44498172a(15) =157331199a(16) =557814747a(17) =1973795538a(18) =6994128261a(19) =24758288103a(20) =87705442452a(21) =310530035379