A078752 Least m>n such that phi(m) >= 2*phi(n), where phi is Euler's totient function (A000010).

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

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: A099536 A345001 A082434 * A343045 A343041 A124115

Adjacent sequences: A078749 A078750 A078751 * A078753 A078754 A078755

Keyword

nonn

Author

Reinhard Zumkeller, Dec 22 2002

Status

approved