A091439 Least k such that k/phi(k) >= n, where phi is Euler's totient function.

1, 2, 6, 210, 30030, 223092870, 13082761331670030, 3217644767340672907899084554130, 1492182350939279320058875736615841068547583863326864530410

Offset

1,2

Comments

These are all primorial numbers (A002110).

It appears that the primorial index of a(n) is A256968(n-1) for n>=1. - Michel Marcus, Oct 07 2019

Links

Table of n, a(n) for n=1..9.

Eric Weisstein's World of Mathematics, Totient Function

Mathematica

Table[prod=1; i=0; While[prod<n, i++; prod=prod/(1-1/Prime[i])]; Times@@Prime[Range[i]], {n, 1, 9}]

Prog

(PARI) a(n) = my(p=1, i=0); while(p<n, i++; p = p/(1-1/prime(i))); prod(k=1, i, prime(k)); \\ Michel Marcus, Oct 07 2019

Crossrefs

Cf. A002110, A091456 (n * phi(k) < k).

Sequence in context: A302344 A156517 A333944 * A285102 A285101 A361086

Adjacent sequences: A091436 A091437 A091438 * A091440 A091441 A091442

Keyword

easy,nonn

Author

T. D. Noe, Jan 09 2004

Status

approved