A069549 Smallest composite k such that phi(k) > k*(1-1/n).

4, 4, 9, 25, 25, 49, 49, 121, 121, 121, 121, 169, 169, 289, 289, 289, 289, 361, 361, 529, 529, 529, 529, 841, 841, 841, 841, 841, 841, 961, 961, 1369, 1369, 1369, 1369, 1369, 1369, 1681, 1681, 1681, 1681, 1849, 1849, 2209, 2209, 2209, 2209, 2809, 2809, 2809

Offset: 1

Author

Benoit Cloitre, Apr 21 2002

Keywords

• easy
• nonn

Comments

Or, least composite k such that k is coprime to the n-1 numbers k+1 ... k+n-1. E.g., a(4) = 25 because 25 is coprime to 26, 27 and 28. - Amarnath Murthy, Apr 20 2004

Crossrefs

Cf. A000010 (phi), A007918, A052349.

Programs

Mathematica

a[n_] := NextPrime[n-1]^2; Array[a, 50] (* Amiram Eldar, May 08 2025 *)

PARI

a(n) = nextprime(n)^2; \\ Amiram Eldar, May 08 2025

Formula

a(n) = nextprime(n)^2 = A007918(n)^2.

Extensions

Edited by David Wasserman, Apr 23 2007