a(n) = floor(4^n/(2+2*cos(2*Pi/7))^n).

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =2a(5) =2a(6) =3a(7) =4a(8) =5a(9) =6a(10) =8a(11) =9a(12) =12a(13) =15a(14) =18a(15) =22a(16) =28a(17) =34a(18) =42a(19) =52a(20) =64a(21) =79a(22) =98a(23) =121a(24) =149a(25) =183a(26) =226a(27) =279a(28) =343a(29) =423