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A091456 Least number k such that n * phi(k) < k, where phi is Euler's totient function. 4

%I #17 Jan 13 2020 11:29:11

%S 2,6,30,210,30030,223092870,13082761331670030,

%T 3217644767340672907899084554130,

%U 1492182350939279320058875736615841068547583863326864530410

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

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

%o (PARI) a(n) = {k = 1; while (n*eulerphi(k) >= k, k++); k;} \\ _Michel Marcus_, Sep 25 2013

%o (PARI) a(n)=my(k=1);forprime(p=2,,if(n*eulerphi(k)<k,return(k),k*=p)) \\ _Charles R Greathouse IV_, Sep 25 2013

%Y Subsequence of A002110. Cf. A000010, A054741, A073087, A091439 (n * phi(k) <= k).

%K nonn

%O 1,1

%A _Robert G. Wilson v_, Jan 10 2004

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Last modified March 28 16:12 EDT 2024. Contains 371254 sequences. (Running on oeis4.)