a(n) = floor(6^n/(2+2*cos(Pi/9))^n).

Terms

a(0) =1a(1) =1a(2) =2a(3) =3a(4) =5a(5) =8a(6) =13a(7) =21a(8) =32a(9) =50a(10) =78a(11) =121a(12) =187a(13) =289a(14) =448a(15) =693a(16) =1072a(17) =1658a(18) =2564a(19) =3966a(20) =6134a(21) =9487a(22) =14673a(23) =22695a(24) =35101a(25) =54288a(26) =83964a(27) =129862a(28) =200850a(29) =310643