a(n) is the smallest index m such that Sum_{k=2..m} 1/PrimePi(k) >= n, where PrimePi()=A000720().

Terms

a(0) =2a(1) =4a(2) =8a(3) =12a(4) =18a(5) =27a(6) =37a(7) =51a(8) =68a(9) =89a(10) =116a(11) =147a(12) =186a(13) =232a(14) =287a(15) =352a(16) =428a(17) =518a(18) =623a(19) =745a(20) =887a(21) =1050a(22) =1240a(23) =1456a(24) =1704a(25) =1987a(26) =2309a(27) =2674a(28) =3090a(29) =3557