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

Terms

a(0) =1a(1) =3a(2) =-6a(3) =-33a(4) =21a(5) =318a(6) =129a(7) =-2733a(8) =-3894a(9) =20703a(10) =55749a(11) =-130578a(12) =-632319a(13) =542883a(14) =6233754a(15) =1347807a(16) =-54755979a(17) =-66886242a(18) =425917569a(19) =1027893747a(20) =-2805364374a(21) =-12056408097a(22) =13191871269a(23) =121699544142a(24) =2972702721