a(n) = floor(6^n/(3+sqrt(3))^n).

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =2a(5) =3a(6) =4a(7) =5a(8) =6a(9) =8a(10) =10a(11) =13a(12) =17a(13) =21a(14) =27a(15) =35a(16) =44a(17) =56a(18) =71a(19) =90a(20) =115a(21) =146a(22) =185a(23) =235a(24) =298a(25) =378a(26) =479a(27) =607a(28) =770a(29) =977