a(n) = floor(((sqrt(sqrt(3))^3)/sqrt(Pi))^n).

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =2a(5) =3a(6) =4a(7) =5a(8) =7a(9) =9a(10) =12a(11) =15a(12) =20a(13) =26a(14) =33a(15) =43a(16) =56a(17) =72a(18) =92a(19) =119a(20) =153a(21) =197a(22) =253a(23) =325a(24) =419a(25) =539a(26) =693a(27) =891a(28) =1146a(29) =1474