A091456 Least number k such that n * phi(k) < k, where phi is Euler's totient function.

2, 6, 30, 210, 30030, 223092870, 13082761331670030, 3217644767340672907899084554130, 1492182350939279320058875736615841068547583863326864530410

Offset: 1

Author

Robert G. Wilson v, Jan 10 2004

Keywords

• nonn

Comments

By Mertens' theorem and the Prime Number Theorem log log a(n) ~ n / e^gamma. - Charles R Greathouse IV, Sep 07 2012

Links

• Amiram Eldar, Table of n, a(n) for n = 1..13

Crossrefs

Subsequence of A002110.

Cf. A000010, A005579, A054741, A073087, A091439 (n * phi(k) <= k).

Programs

PARI

a(n) = {k = 1; while (n*eulerphi(k) >= k, k++); k;} \\ Michel Marcus, Sep 25 2013

PARI

a(n)=my(k=1);forprime(p=2,,if(n*eulerphi(k)Charles R Greathouse IV, Sep 25 2013

Formula

a(n) = A002110(A005579(n)). - Amiram Eldar, Nov 30 2024