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A069237 Composite n such that tau(n) divides phi(n), where tau(n) is the number of divisors of n and phi(n) the Euler totient function. 1
8, 9, 10, 15, 18, 21, 24, 26, 28, 30, 33, 34, 35, 39, 40, 45, 49, 51, 52, 55, 56, 57, 58, 63, 65, 69, 70, 72, 74, 76, 77, 78, 82, 84, 85, 87, 88, 90, 91, 93, 95, 98, 99, 102, 104, 105, 106, 108, 110, 111, 115, 117, 119, 120, 122, 123, 124, 125, 126, 128, 129, 130, 133 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Includes A057388 and 2*A002144. - Robert Israel, Jan 05 2018

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

MAPLE

filter:= n -> not isprime(n) and numtheory:-phi(n) mod numtheory:-tau(n)=0:

select(filter, [$4..1000]); # Robert Israel, Jan 05 2018

MATHEMATICA

nn=200; Rest[Select[Complement[Range[nn], Prime[Range[PrimePi[nn]]]], Divisible[ EulerPhi[#], DivisorSigma[0, #]]&]] (* Harvey P. Dale, Mar 31 2011 *)

CROSSREFS

Composite numbers in A003601.

Cf. A002144, A057388.

Sequence in context: A072381 A046415 A091417 * A334728 A070480 A135043

Adjacent sequences:  A069234 A069235 A069236 * A069238 A069239 A069240

KEYWORD

easy,nonn

AUTHOR

Benoit Cloitre, Apr 13 2002

STATUS

approved

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Last modified October 20 10:00 EDT 2020. Contains 337900 sequences. (Running on oeis4.)