Floor(sqrt(3*2^n)).

Terms

a(0) =1a(1) =2a(2) =3a(3) =4a(4) =6a(5) =9a(6) =13a(7) =19a(8) =27a(9) =39a(10) =55a(11) =78a(12) =110a(13) =156a(14) =221a(15) =313a(16) =443a(17) =627a(18) =886a(19) =1254a(20) =1773a(21) =2508a(22) =3547a(23) =5016a(24) =7094a(25) =10033a(26) =14188a(27) =20066a(28) =28377a(29) =40132