a(n) = 2*a(n-1) + 5*a(n-2), with a(0) = 0, a(1) = 3.

Terms

a(0) =0a(1) =3a(2) =6a(3) =27a(4) =84a(5) =303a(6) =1026a(7) =3567a(8) =12264a(9) =42363a(10) =146046a(11) =503907a(12) =1738044a(13) =5995623a(14) =20681466a(15) =71341047a(16) =246089424a(17) =848884083a(18) =2928215286a(19) =10100850987a(20) =34842778404a(21) =120189811743a(22) =414593515506