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A078752 Least m>n such that phi(m) >= 2*phi(n), where phi is Euler's totient function (A000010). 1
3, 3, 5, 5, 11, 7, 13, 11, 13, 11, 23, 13, 29, 17, 17, 17, 37, 19, 37, 23, 29, 23, 47, 25, 41, 29, 37, 29, 59, 31, 61, 37, 41, 37, 53, 37, 73, 41, 53, 41, 83, 43, 89, 47, 53, 47, 97, 49, 89, 53, 67, 53, 107, 55, 83, 59, 73, 59, 127, 61, 127, 67, 73, 67, 97, 67, 137, 71, 89, 71 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

For odd primes p: a(p-1) = p; the converse is not true, as e.g. a(25-1)=25.

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

MATHEMATICA

epm[n_]:=Module[{m=n+1, epn2=2EulerPhi[n]}, While[EulerPhi[m]<epn2, m++]; m]; Array[epm, 70] (* Harvey P. Dale, Apr 13 2012 *)

PROG

(PARI) a(n)=my(t=2*eulerphi(n), m=max(n, t)); while(eulerphi(m++)<t, ); m \\ Charles R Greathouse IV, Feb 21 2013

CROSSREFS

Sequence in context: A241508 A099536 A082434 * A124115 A124114 A077893

Adjacent sequences:  A078749 A078750 A078751 * A078753 A078754 A078755

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Dec 22 2002

STATUS

approved

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Last modified May 23 11:05 EDT 2019. Contains 323513 sequences. (Running on oeis4.)