A122489 Partial sums of A111939 (= number of primes < semiprime(n)).

2, 5, 9, 13, 19, 25, 33, 41, 50, 59, 70, 81, 92, 104, 116, 130, 145, 160, 176, 192, 208, 226, 244, 263, 284, 305, 327, 350, 373, 396, 420, 444, 468, 492, 519, 548, 578, 608, 638, 668, 698, 728, 759, 791, 823, 857, 891, 925, 959, 993, 1029, 1066, 1103, 1140

Offset

1,1

Comments

Perfect powers occur at the following terms:

a(3) = 9 = 3^2

a(6) = 25 = 5^2

a(12) = 81 = 3^4

a(74) = 2025 = 45^2

a(2072) = 1062961 = 1031^2

a(43881) = 392713489 = 19817^2

a(134249) = 3497963832 = 1518^3

a(372727) = 25930982961 = 161031^2

a(1196234) = 257007427681 = 506959^2

a(1449506) = 375159925009 = 612503^2

a(5226094) = 4704717169296 = 2169036^2

a(8342271) = 11846166214276 = 3441826^2

a(62507725) = 635490555087844 = 25208938^2

a(91695024) = 1356954402007044 = 36836862^2

No further perfect powers through a(10^8).

Links

Table of n, a(n) for n=1..54.

Mathematica

t=PrimePi@Select[Range@218, Plus @@ Last /@ FactorInteger@# == 2 &]; Table[Sum[t[[i]], {i, n}], {n, Length[t]}] (* Ray Chandler, Sep 20 2006 *)

Crossrefs

Partial sums of A111939(n).

Sequence in context: A267531 A219647 A129726 * A120615 A038707 A290140

Adjacent sequences: A122486 A122487 A122488 * A122490 A122491 A122492

Keyword

easy,nonn

Author

Giovanni Teofilatto, Sep 16 2006

Extensions

Edited and corrected by Ray Chandler, Sep 20 2006

Status

approved