Powers of cube root of 20 rounded up.

Terms

a(0) =1a(1) =3a(2) =8a(3) =20a(4) =55a(5) =148a(6) =400a(7) =1086a(8) =2948a(9) =8000a(10) =21716a(11) =58945a(12) =160000a(13) =434307a(14) =1178891a(15) =3200000a(16) =8686137a(17) =23577802a(18) =64000000a(19) =173722728a(20) =471556032a(21) =1280000000a(22) =3474454550a(23) =9431120637a(24) =25600000000a(25) =69489090985a(26) =188622412731a(27) =512000000000