Powers of sqrt(12) rounded down.

Terms

a(0) =1a(1) =3a(2) =12a(3) =41a(4) =144a(5) =498a(6) =1728a(7) =5985a(8) =20736a(9) =71831a(10) =248832a(11) =861979a(12) =2985984a(13) =10343751a(14) =35831808a(15) =124125023a(16) =429981696a(17) =1489500287a(18) =5159780352a(19) =17874003451a(20) =61917364224a(21) =214488041413a(22) =743008370688