

A094757


Least k <= n such that n*pi(k) = k*pi(n), where pi(n) is the number of primes <= n (A000720).


3



1, 2, 3, 2, 5, 2, 7, 2, 9, 10, 11, 12, 13, 14, 10, 16, 17, 18, 19, 10, 21, 22, 23, 16, 25, 26, 27, 28, 29, 27, 31, 32, 27, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 40, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 56, 64, 65, 66, 67, 68, 69, 70, 71, 72
(list;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

1,2


COMMENTS

Conjecture: For every n there exists a k different from n (possibly k > n) such that n*pi(k) = k*pi(n). (Amarnath Murthy)


LINKS

Table of n, a(n) for n=1..72.


EXAMPLE

a(15) = 10 as 15*pi(10) = 15*4 = 60 = 10*pi(15) = 10*6.


PROG

(PARI) {m=72; pi=vector(m, n, omega(n!)); for(n=1, m, k=1; while(n*pi[k]!=k*pi[n], k++); print1(k, ", "))}


CROSSREFS

Cf. A095299 for n such that a(n) < n.
Cf. A000720, A094758, A094759.
Sequence in context: A007387 A105222 A280503 * A095171 A270443 A096776
Adjacent sequences: A094754 A094755 A094756 * A094758 A094759 A094760


KEYWORD

nonn


AUTHOR

Amarnath Murthy, May 30 2004


EXTENSIONS

Edited and extended by Klaus Brockhaus, Jun 01 2004


STATUS

approved



