Powers of sqrt(12) rounded up.

Terms

a(0) =1a(1) =4a(2) =12a(3) =42a(4) =144a(5) =499a(6) =1728a(7) =5986a(8) =20736a(9) =71832a(10) =248832a(11) =861980a(12) =2985984a(13) =10343752a(14) =35831808a(15) =124125024a(16) =429981696a(17) =1489500288a(18) =5159780352a(19) =17874003452a(20) =61917364224a(21) =214488041414a(22) =743008370688