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A067800 Nonprime n such that phi(n) > n/2. 4
1, 9, 15, 21, 25, 27, 33, 35, 39, 45, 49, 51, 55, 57, 63, 65, 69, 75, 77, 81, 85, 87, 91, 93, 95, 99, 111, 115, 117, 119, 121, 123, 125, 129, 133, 135, 141, 143, 145, 147, 153, 155, 159, 161, 169, 171, 175, 177, 183, 185, 187, 189, 201, 203, 205, 207, 209, 213, 215 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
Sequence is similar to A014076(n) giving odd nonprimes. Only 3 terms = 105, 165, 195 are not in the sequence among 59 terms < 210.
Cototient[m] > totient[m] equivalent to 2phi[m] < m; the missing terms mentioned here seem to form A036798. - Labos Elemer, May 08 2003
The number 9075 is not in this sequence, is in A014076 and is not in A036798, which means that the missing terms mentioned here do not form A036798 (cf. A118700). - R. J. Mathar, Aug 08 2007
LINKS
MATHEMATICA
Select[Range[250], !PrimeQ[#]&&EulerPhi[#]>#/2&] (* Harvey P. Dale, Aug 29 2021 *)
CROSSREFS
Sequence in context: A071904 A326586 A014076 * A155474 A100819 A046446
KEYWORD
nonn
AUTHOR
Benoit Cloitre, Feb 07 2002
STATUS
approved

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Last modified March 28 05:39 EDT 2024. Contains 371235 sequences. (Running on oeis4.)