a(n) = ceiling( Pi^(n/3) ).

Terms

a(0) =2a(1) =3a(2) =4a(3) =5a(4) =7a(5) =10a(6) =15a(7) =22a(8) =32a(9) =46a(10) =67a(11) =98a(12) =143a(13) =209a(14) =307a(15) =449a(16) =657a(17) =962a(18) =1409a(19) =2063a(20) =3021a(21) =4424a(22) =6479a(23) =9489a(24) =13897a(25) =20354a(26) =29810a(27) =43659a(28) =63942a(29) =93649