a(n) = PrimePi(n^3) - PrimePi(n)^3, where PrimePi = A000720.

Terms

a(0) =0a(1) =3a(2) =1a(3) =10a(4) =3a(5) =20a(6) =4a(7) =33a(8) =65a(9) =104a(10) =92a(11) =144a(12) =111a(13) =184a(14) =260a(15) =348a(16) =313a(17) =422a(18) =370a(19) =495a(20) =635a(21) =786a(22) =728a(23) =904a(24) =1092a(25) =1291a(26) =1498a(27) =1731a(28) =1707a(29) =1961