Powers of cube root of 21 rounded down.

Terms

a(0) =1a(1) =2a(2) =7a(3) =21a(4) =57a(5) =159a(6) =441a(7) =1216a(8) =3356a(9) =9261a(10) =25550a(11) =70491a(12) =194481a(13) =536558a(14) =1480323a(15) =4084101a(16) =11267724a(17) =31086798a(18) =85766121a(19) =236622224a(20) =652822776a(21) =1801088541a(22) =4969066719a(23) =13709278306a(24) =37822859361a(25) =104350401110a(26) =287894844440a(27) =794280046581