a(n) = floor(e^(n/3)).

Terms

a(0) =1a(1) =1a(2) =2a(3) =3a(4) =5a(5) =7a(6) =10a(7) =14a(8) =20a(9) =28a(10) =39a(11) =54a(12) =76a(13) =106a(14) =148a(15) =207a(16) =289a(17) =403a(18) =563a(19) =785a(20) =1096a(21) =1530a(22) =2135a(23) =2980a(24) =4160a(25) =5806a(26) =8103a(27) =11308a(28) =15782a(29) =22026