A000879 Number of primes < prime(n)^2.

2, 4, 9, 15, 30, 39, 61, 72, 99, 146, 162, 219, 263, 283, 329, 409, 487, 519, 609, 675, 705, 811, 886, 1000, 1163, 1252, 1294, 1381, 1423, 1523, 1877, 1976, 2141, 2190, 2489, 2547, 2729, 2915, 3043, 3241, 3436, 3512, 3868, 3945, 4089, 4164, 4627, 5106

Offset: 1

Author

gandalf(AT)hrn.office.ssi.net (James D. Ausfahl)

Keywords

• nonn

Comments

a(n) is the least index i such that A052180(i) = prime(n). - Labos Elemer, May 14 2003

Number of primes determined at the n-th step of the sieve of Eratosthenes. - Jean-Christophe Hervé, Oct 21 2013

There are only 3 squares in the current data: 4, 9, 7745089. - Michel Marcus, Apr 07 2018

There are no other squares up to a(780000). - Giovanni Resta, Apr 09 2018

Links

• Donovan Johnson, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A050216 (first differences), A089609, A052180, A000720, A001248, A000885, A054270 (primes of rank a(n)).

Programs

Mathematica

PrimePi[Prime[Range[50]]^2] (* Harvey P. Dale, Jan 16 2013 *)

PARI

a(n) = primepi(prime(n)^2); \\ Michel Marcus, Oct 28 2013

Formula

a(n) = A000720(A001248(n)). - Michel Marcus, Apr 07 2018

Extensions

Edited by Ralf Stephan, Aug 24 2004