A054270 Largest prime below prime(n)^2 (A001248).

3, 7, 23, 47, 113, 167, 283, 359, 523, 839, 953, 1367, 1669, 1847, 2207, 2803, 3469, 3719, 4483, 5039, 5323, 6229, 6883, 7919, 9403, 10193, 10607, 11447, 11867, 12763, 16127, 17159, 18757, 19319, 22193, 22787, 24631, 26561, 27883, 29927, 32029

Offset: 1

Author

Labos Elemer, May 05 2000

Keywords

• nonn

Comments

For n > 1, the n-1 first primes determine the primes up to a(n). This is how the Sieve of Eratosthenes works. - Jean-Christophe Hervé, Oct 21 2013

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000040, A000879, A001248, A054271.

Programs

Maple

seq(prevprime(ithprime(i)^2),i=1..100); # Robert Israel, May 04 2020

Mathematica

NextPrime[Prime[Range[50]]^2,-1] (* Harvey P. Dale, May 19 2016 *)

PARI

a(n) = precprime(prime(n)^2); \\ Michel Marcus, Dec 13 2013

Formula

a(n) = Max[prime q: q < prime(n)^2].

a(n) = prime(A000879(n)) = A000040(A000879(n)). - Jean-Christophe Hervé, Oct 21 2013